Methods and intermediates for the synthesis of porphyrins

ABSTRACT

A method of making a porphyrin (I) is carried out by condensing (i) a bis(imino)dipyrromethane of Formula II: 
                         
with (ii) a dipyrromethaneto produce a reaction product; then (b) optionally oxidizing said reaction product with an oxidizing agent; and then (c) optionally demetallating said reaction product to produce the porphyrin. Methods of making compounds of Formula II are also described.

RELATED APPLICATIONS

This application claims priority to and is a divisional of U.S. patentapplication Ser. No. 11/193,562, filed Jul. 29, 2005 now U.S. Pat. No.7,582,751, now allowed, and is related to Jonathan S. Lindsey, MasahikoTaniguchi, and Dazhong Fan, U.S. patent application Ser. No. 11/192,934,Methods and Intermediates for the Synthesis of Porphyrins, filed Jul.29, 2005, now issued as U.S. Pat. 7,501,508, the disclosure of each ofwhich is incorporated by reference herein in its entirety.

This invention was made with US Government support under Grant NumberGM36238 from the National Institutes of Health. The Government hascertain rights to this invention.

FIELD OF THE INVENTION

The present invention concerns methods for making porphyrins, includingbut not limited to trans-A,B-porphyrins, with bis(imine)dipyrromethaneintermediates.

BACKGROUND OF THE INVENTION

Porphyrinic macrocycles bearing distinct patterns of substituents areimportant building blocks in diverse applications. Two distinctstrategies have been applied to control the pattern of substituentsabout the porphyrin perimeter: (1) pre-arranging substituents inprecursors to the porphyrinic macrocycle, or (2) preparing a porphyrinwith a limited number of substituents and then introducing additionalsubstituents by derivatization of the porphyrin. As an example of theformer, the acid-catalyzed condensation of a dipyrromethane-dicarbinol+adipyrromethane followed by oxidation provides a rational synthesis ofABCD-porphyrins [1]. The derivatization procedures in the latterapproach include (i) halogenation of the porphyrin meso position andsubsequent C—C bond formation (e.g., Suzuki, Heck, Sonogashira, orrelated palladium-mediated coupling reactions)[2] or (ii) nucleophilicattack of an alkyl or aryl lithium reagent followed by DDQ oxidation[3].

Porphyrins bearing only one or two meso-substituents (i.e., trans-AB-,trans-A₂-, A-porphyrins) are of considerable interest owing to theircompact size. A variety of trans-AB-porphyrins have been preparedalthough most also contain a full complement of β-substituents [4].Porphyrins bearing only one or two meso substituents and lackingβ-substituents in principle are available via the same methodology usedto prepare ABCD-porphyrins, but traditionally the syntheses have beencarried out by alternative routes. All known routes to trans-AB-,trans-A₂-, and A-porphyrins are described below.

trans-AB-porphyrins: Synthetic approaches to β-unsubstitutedtrans-AB-porphyrins are illustrated based on the synthetic method(statistical or rational) and the substitution pattern of the precursors(Scheme 1, Routes 1-6). Statistical methods (Routes 1 [5] and 2 [6]) donot require functionalization of the dipyrromethane but result in amixture of three porphyrins that requires chromatographic purification.The [2+2] MacDonald-type condensations of dipyrromethane derivativesinclude a dipyrromethane-1,9-dicarbinol+a dipyrromethane (Route 3,demonstrated for β-substituted substrates only) [7], a 5-substituteddiformyldipyrromethane+a 5-substituted dipyrromethane (Route 4) [8], anda 5-substituted 1,9-bis(hydroxymethyl)dipyrromethane+a 5-substituteddipyrromethane (Route 5) [9]. In each case, the acid catalysis requiredto facilitate reaction at the α-substituent (e.g., formyl orhydroxymethyl group) often results in undesired rearrangement of thedipyrromethane reactants or oligopyrromethane intermediates, resultingin the formation of undesired porphyrinic macrocycles (i.e., scrambling)[9]. A related route (Route 6) developed in parallel with the workherein employs a 1,9-bis(N,N-dimethylaminomethyl)dipyrromethane+adipyrromethane [10].

trans-A₂-porphyrins: The synthesis of trans-A₂-porphyrins can beachieved via the same routes as for trans-AB-porphyrins (where A=B inwhich case routes 1-5 are all rational) [9, 11, 12], as well as theself-condensation of a dipyrromethane-1-carbinol [12]. The simplest andmost effective approach entails route 1, where dipyrromethane itself isreacted with aldehyde A [11].

A-porphyrins: Rational synthetic methods for preparing porphyrinsbearing a single meso substituent have been applied exclusively withβ-substituted dipyrromethanes (Scheme 2): (1) MacDonald [2+2]condensation of a diformyldipyrromethane+a dipyrromethane (Route 7)[13-15], and (2) a biladiene+aldehyde (Route 8) [15, 16]. A statisticalsynthesis afforded a β-unsubstituted A-porphyrin in 2-12% yield togetherwith trans-A₂-porphyrin byproducts (Route 9) [17]. An alternativeapproach to introduce a single meso substituent entails substitution ofporphine [18, 19]. Porphyrins bearing a single meso substituent alsohave resulted as byproducts of scrambling processes withmeso-unsubstituted dipyrromethanes [20,21] or tripyrrane [19].

In attempting to apply the methodology developed for the synthesis ofABCD-porphyrins to porphyrins bearing lesser substitution (e.g.,trans-AB-, A-porphyrins), we were surprised to find that dipyrromethanereactants bearing a primary carbinol (route 5, Scheme 1) resulted in lowyields of porphyrin (<5%) and the occurrence of scrambling [9]. Bycontrast, dipyrromethanes bearing a secondary carbinol (alkyl or aryl)typically afford yields of 10-35% and proceed without scrambling.Although such shortcomings can be circumvented in the synthesis oftrans-AB-porphyrins through use of route 3, a number of substituents(mesityl [1], branched alkyl [22]) cannot be accommodated at thecarbinol position. Moreover, no such solution is available for thesynthesis of A-porphyrins.

We note also that the yields of trans-AB-porphyrins that bearβ-substituents are often quite reasonable. The good yields areattributed to the following factors: (1) lack of a meso substituent atthe dipyrromethane lessens propensity to scrambling, (2) the presence ofβ-substituents at the dipyrromethane enforces conformations inclined tocyclize, and (3) blockage of the β-position leaves the α-position as theonly site available for reaction. These features are absent inβ-unsubstituted trans-AB-porphyrins, and consequently, refined methodsare required for preparing this seemingly simple class of compounds.

SUMMARY OF THE INVENTION

A first aspect of the invention is a method of making a porphyrin ofFormula I:

wherein:

A and B are each independently H, alkyl, alkenyl, alkynyl, cycloalkyl,cycloalkylalkyl, cycloalkylalkenyl, cycloalkylalkynyl, aryl, arylalkyl,arylalkenyl, arylalkynyl, alkoxy, halo, mercapto, azido, cyano,hydroxyl, nitro, acyl, alkoxy, alkylthio, amino, alkylamino,arylalkylamino, disubstituted amino, acylamino, acyloxy, amide,sulfonamide, urea, alkoxylacylamino, aminoacyloxy, hydrophilic groups,surface attachment groups, cross-coupling groups or bioconjugatablegroups;

R¹ is selected from the group consisting of H, alkyl and aryl;

R², R³, R⁴, R⁵, R⁷, R⁸, R⁹, and R¹⁰ are each independently selected fromthe group consisting of H, halo, loweralkoxy, and loweralkylthio; and

M is a metal or a pair of hydrogen atoms;

said method comprising:

(a) condensing (i) a bis(imino)dipyrromethane of Formula II:

wherein:

R is alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl,cycloalkylalkenyl, cycloalkylalkynyl, aryl, arylalkyl, arylalkenyl,arylalkynyl, alkoxy, or acyl; and

A, R¹, R², R³, R⁴, and R⁵ are as given above, with (ii) a dipyrromethaneof Formula III:

wherein B, R⁷, R⁸, R⁹ and R¹⁰ are as given above, in an organic solventcontaining a metal salt to produce a reaction product; then (b)optionally oxidizing said reaction product with an oxidizing agent; andthen (c) optionally demetallating said reaction product to produce theporphyrin of Formula I.

A further aspect of the invention is a method of making a compound ofFormula II:

wherein R, R¹, R², R³, R⁴, R⁵ and A are as given above, comprisingreacting a dipyrromethane of Formula IV:

wherein A, R¹, R², R³, R⁴ and R⁵ are as given above

with a compound of Formula V:R—NH₂  (V)wherein R is as given above in an organic solvent to produce saidcompound of Formula II.

The foregoing and other objects and aspects of the invention areexplained in greater detail in the drawings herein and the specificationset forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. (A) The effect of the concentration of dipyrromethane species[3a] and [1b] in porphyrin formation [Zn(OAc)₂ (10 equiv) in EtOH atreflux in air for 5 h; data points are 1, 3.16, 10, 31.6, 100, and 316mM]. The yield was determined by absorption spectroscopy in THF. (B)Yield of porphyrin Zn4ab as a function of time upon condensation of3a+1b{[3a]=[1b]=10 mM, Zn(OAc)₂ (10 equiv) in EtOH at reflux in air}.The yield was determined by absorption spectroscopy in THF.

FIG. 2. Reaction intermediates observed on the basis of studies withphenyl (3a), H (3j), and pentyl (3l) substitutedbis(imino)dipyrromethanes. All bis(imino)dipyrromethanes examinedundergo reversible formation of the complex (3)₂Zn₂. Thosebis(imino)dipyrromethanes bearing aryl (but not alkyl or H) groupsundergo the processes shown outside the dashed box. Note that simplechromatographic purification afforded the desired zinc porphyrin (4)free of reactants (3+dipyrromethane) and any intermediates or byproductssuch as 5, (3)₂Zn₂, and (5)₂Zn₂.

FIG. 3. Absorption spectral traces of the reaction of 3a (31.6 mM) upontreatment with Zn(OAc)₂ (10 equiv) in ethanol. (A) Reaction at roomtemperature, showing predominant formation of (3a)₂Zn₂ within 1 min. (B)Reaction at reflux, showing formation of (3a)₂Zn₂ and conversion largelyto bis(dipyrrinato)zinc(II) complex (5a)₂Zn. Note that the amount ofbis(dipyrrinato)zinc(II) complex (5a)₂Zn can be quite small despite theintense color of the mixture, due to the sizable molar absorptioncoefficient expected for such species [43].

The present invention is explained in greater detail in thespecification set forth below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

“Halo” as used herein refers to any suitable halogen, including —F, —Cl,—Br, and —I.

“Mercapto” as used herein refers to an —SH group.

“Azido” as used herein refers to an —N₃ group.

“Cyano” as used herein refers to a —CN group.

“Hydroxyl” as used herein refers to an —OH group.

“Nitro” as used herein refers to an —NO₂ group.

“Alkyl” as used herein alone or as part of another group, refers to astraight or branched chain hydrocarbon containing from 1 to 10, 20, 40or 50 carbon atoms. Representative examples of alkyl include, but arenot limited to, methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl,iso-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl,3-methylhexyl, 2,2-dimethylpentyl, 2,3-dimethylpentyl, n-heptyl,n-octyl, n-nonyl, n-decyl, and the like. “Lower alkyl” as used herein,is a subset of alkyl, in some embodiments preferred, and refers to astraight or branched chain hydrocarbon group containing from 1 to 4carbon atoms. Representative examples of lower alkyl include, but arenot limited to, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl,tert-butyl, and the like. The term “akyl” or “loweralkyl” is intended toinclude both substituted and unsubstituted alkyl or loweralkyl unlessotherwise indicated and these groups may be substituted with groupsselected from halo, alkyl, haloalkyl, alkenyl, alkynyl, cycloalkyl,cycloalkylalkyl, aryl, arylalkyl, heterocyclo, heterocycloalkyl,hydroxyl, alkoxy, alkenyloxy, alkynyloxy, haloalkoxy, cycloalkoxy,cycloalkylalkyloxy, aryloxy, arylalkyloxy, heterocyclooxy,heterocycloalkyloxy, mercapto, alkyl-S(O)_(m), haloalkyl-S(O)_(m),alkenyl-S(O)_(m), alkynyl-S(O)_(m), cycloalkyl-S(O)_(m),cycloalkylalkyl-S(O)_(m), aryl-S(O)_(m), arylalkyl-S(O)_(m),heterocyclo-S(O)_(m), heterocycloalkyl-S(O)_(m), amino, alkylamino,alkenylamino, alkynylamino, haloalkylamino, cycloalkylamino,cycloalkylalkylamino, arylamino, arylalkylamino, heterocycloamino,heterocycloalkylamino, disubstituted-amino, acylamino, acyloxy, ester,amide, sulfonamide, urea, alkoxyacylamino, aminoacyloxy, nitro or cyanowhere m=0, 1 or 2.

“Alkenyl” as used herein alone or as part of another group, refers to astraight or branched chain hydrocarbon containing from 1 to 10 carbonatoms (or in loweralkenyl 1 to 4 carbon atoms) which include 1 to 4double bonds in the normal chain. Representative examples of alkenylinclude, but are not limited to, vinyl, 2-propenyl, 3-butenyl,2-butenyl, 4-pentenyl, 3-pentenyl, 2-hexenyl, 3-hexenyl, 2,4-heptadiene,and the like. The term “alkenyl” or “loweralkenyl” is intended toinclude both substituted and unsubstituted alkenyl or loweralkenylunless otherwise indicated and these groups may be substituted withgroups as described in connection with alkyl and loweralkyl above.

“Alkynyl” as used herein alone or as part of another group, refers to astraight or branched chain hydrocarbon containing from 1 to 10 carbonatoms (or in loweralkynyl 1 to 4 carbon atoms) which include 1 triplebond in the normal chain. Representative examples of alkynyl include,but are not limited to, 2-propynyl, 3-butynyl, 2-butynyl, 4-pentynyl,3-pentynyl, and the like. The term “alkynyl” or “loweralkynyl” isintended to include both substituted and unsubstituted alkynyl orloweralknynyl unless otherwise indicated and these groups may besubstituted with the same groups as set forth in connection with alkyland loweralkyl above.

“Alkoxy” as used herein alone or as part of another group, refers to analkyl or loweralkyl group, as defined herein, appended to the parentmolecular moiety through an oxy group, —O—. Representative examples ofalkoxy include, but are not limited to, methoxy, ethoxy, propoxy,2-propoxy, butoxy, tert-butoxy, pentyloxy, hexyloxy and the like.

“Acyl” as used herein alone or as part of another group refers to a—C(O)R radical, where R is any suitable substituent such as aryl, alkyl,alkenyl, alkynyl, cycloalkyl or other suitable substituent as describedherein.

“Haloalkyl” as used herein alone or as part of another group, refers toat least one halogen, as defined herein, appended to the parentmolecular moiety through an alkyl group, as defined herein.Representative examples of haloalkyl include, but are not limited to,chloromethyl, 2-fluoroethyl, trifluoromethyl, pentafluoroethyl,2-chloro-3-fluoropentyl, and the like.

“Alkylthio” as used herein alone or as part of another group, refers toan alkyl group, as defined herein, appended to the parent molecularmoiety through a thio moiety, as defined herein. Representative examplesof alkylthio include, but are not limited, methylthio, ethylthio,tert-butylthio, hexylthio, and the like.

“Aryl” as used herein alone or as part of another group, refers to amonocyclic carbocyclic ring system or a bicyclic carbocyclic fused ringsystem having one or more aromatic rings. “Aryl” includes aromaticheterocyclic groups or heterocyclo groups as discussed below.Representative examples of aryl include, azulenyl, indanyl, indenyl,naphthyl, phenyl, tetrahydronaphthyl, and the like. The term “aryl” isintended to include both substituted and unsubstituted aryl unlessotherwise indicated and these groups may be substituted with the samegroups as set forth in connection with alkyl and loweralkyl above.

“Arylalkyl” as used herein alone or as part of another group, refers toan aryl group, as defined herein, appended to the parent molecularmoiety through an alkyl group, as defined herein. Representativeexamples of arylalkyl include, but are not limited to, benzyl,2-phenylethyl, 3-phenylpropyl, 2-naphth-2-ylethyl, and the like.

“Amino” as used herein means the radical —NH₂.

“Alkylamino” as used herein alone or as part of another group means theradical —NHR, where R is an alkyl group.

“Arylalkylamino” as used herein alone or as part of another group meansthe radical —NHR, where R is an arylalkyl group.

“Disubstituted-amino” as used herein alone or as part of another groupmeans the radical —NR_(a)R_(b), where R_(a) and R_(b) are independentlyselected from the groups alkyl, haloalkyl, alkenyl, alkynyl, cycloalkyl,cycloalkylalkyl, aryl, arylalkyl, heterocyclo, heterocycloalkyl.

“Monosubstituted-amino” as used herein alone or as part of another groupmeans the radical —NHR, where R ia selected from the groups alkyl,haloalkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl, aryl,arylalkyl, heterocyclo, heterocycloalkyl.

“Amine” as used herein refers to amino, monosubstituted-amino,disubstituted-amino.

“Acylamino” as used herein alone or as part of another group means theradical —NR_(a)R_(b), where R_(a) is an acyl group as defined herein andR_(b) is selected from the groups hydrogen, alkyl, haloalkyl, alkenyl,alkynyl, cycloalkyl, cycloalkylalkyl, aryl, arylalkyl, heterocyclo,heterocycloalkyl.

“Acyloxy” as used herein alone or as part of another group means theradical —OR, where R is an acyl group as defined herein.

“Ester” as used herein alone or as part of another group refers to a—C(O)OR radical, where R is any suitable substituent such as alkyl,cycloalkyl, alkenyl, alkynyl or aryl.

“Amide” as used herein alone or as part of another group refers to a—C(O)NR_(a)R_(b) radical, where R_(a) and R_(b) are any suitablesubstituent such as alkyl, cycloalkyl, alkenyl, alkynyl or aryl.

“Sulfonamide” as used herein alone or as part of another group refers toa —S(O)₂NR_(a)R_(b) radical, where R_(a) and R_(b) are any suitablesubstituent such as H, alkyl, cycloalkyl, alkenyl, alkynyl or aryl.

“Urea” as used herein alone or as part of another group refers to an—N(R_(c))C(O)NR_(a)R_(b) radical, where R_(a), R_(b) and R_(c) are anysuitable substituent such as H, alkyl, cycloalkyl, alkenyl, alkynyl oraryl.

“Alkoxyacylamino” as used herein alone or as part of another grouprefers to an —N(R_(a))C(O)OR_(b) radical, where R_(a), R_(b) are anysuitable substituent such as H, alkyl, cycloalkyl, alkenyl, alkynyl oraryl.

“Aminoacyloxy” as used herein alone or as part of another group refersto an —OC(O)NR_(a)R_(b) radical, where R_(a) and R_(b) are any suitablesubstituent such as H, alkyl, cycloalkyl, alkenyl, alkynyl or aryl.

“Cycloalkyl” as used herein alone or as part of another group, refers toa saturated or partially unsaturated cyclic hydrocarbon group containingfrom 3, 4 or 5 to 6, 7 or 8 carbons (which carbons may be replaced in aheterocyclic group as discussed below). Representative examples ofcycloalkyl include, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl,cycloheptyl, and cyclooctyl. These rings may be optionally substitutedwith additional substituents as described herein such as halo orloweralkyl. The term “cycloalkyl” is generic and intended to includeheterocyclic groups as discussed below unless specified otherwise.

“Heterocyclic group” or “heterocyclo” as used herein alone or as part ofanother group, refers to an aromatic or nonaromatic (e.g., saturated orpartially unsaturated aliphatic) monocyclic- or a bicyclic-ring system.Monocyclic ring systems are exemplified by any 5 or 6 membered ringcontaining 1, 2, 3, or 4 heteroatoms independently selected from oxygen,nitrogen and sulfur. The 5 membered ring has from 0-2 double bonds andthe 6 membered ring has from 0-3 double bonds. Representative examplesof monocyclic ring systems include, but are not limited to, azetidine,azepine, aziridine, diazepine, 1,3-dioxolane, dioxane, dithiane, furan,imidazole, imidazoline, imidazolidine, isothiazole, isothiazoline,isothiazolidine, isoxazole, isoxazoline, isoxazolidine, morpholine,oxadiazole, oxadiazoline, oxadiazolidine, oxazole, oxazoline,oxazolidine, piperazine, piperidine, pyran, pyrazine, pyrazole,pyrazoline, pyrazolidine, pyridine, pyrimidine, pyridazine, pyrrole,pyrroline, pyrrolidine, tetrahydrofuran, tetrahydrothiophene, tetrazine,tetrazole, thiadiazole, thiadiazoline, thiadiazolidine, thiazole,thiazoline, thiazolidine, thiophene, thiomorpholine, thiomorpholinesulfone, thiopyran, triazine, triazole, trithiane, and the like.Bicyclic ring systems are exemplified by any of the above monocyclicring systems fused to an aryl group as defined herein, a cycloalkylgroup as defined herein, or another monocyclic ring system as definedherein. Representative examples of bicyclic ring systems include but arenot limited to, for example, benzimidazole, benzothiazole,benzothiadiazole, benzothiophene, benzoxadiazole, benzoxazole,benzofuran, benzopyran, benzothiopyran, benzodioxine, 1,3-benzodioxole,cinnoline, indazole, indole, indoline, indolizine, naphthyridine,isobenzofuran, isobenzothiophene, isoindole, isoindoline, isoquinoline,phthalazine, purine, pyranopyridine, quinoline, quinolizine,quinoxaline, quinazoline. tetrahydroisoquinoline, tetrahydroquinoline,thiopyranopyridine, and the like. These rings may be optionallysubstituted with groups selected from halo, alkyl, haloalkyl, alkenyl,alkynyl, cycloalkyl, cycloalkylalkyl, aryl, arylalkyl, heterocyclo,heterocycloalkyl, hydroxyl, alkoxy, alkenyloxy, alkynyloxy, haloalkoxy,cycloalkoxy, cycloalkylalkyloxy, aryloxy, arylalkyloxy, heterocyclooxy,heterocycloalkyloxy, mercapto, alkyl-S(O)_(m), haloalkyl-S(O)_(m),alkenyl-S(O)_(m), alkynyl-S(O)_(m), cycloalkyl-S(O)_(m),cycloalkylalkyl-S(O)_(m), aryl-S(O)_(m), arylalkyl-S(O)_(m),heterocyclo-S(O)_(m), heterocycloalkyl-S(O)_(m), amino, alkylamino,alkenylamino, alkynylamino, haloalkylamino, cycloalkylamino,cycloalkylalkylamino, arylamino, arylalkylamino, heterocycloamino,heterocycloalkylamino, disubstituted-amino, acylamino, acyloxy, ester,amide, sulfonamide, urea, alkoxyacylamino, aminoacyloxy, nitro or cyanowhere m=0, 1 or 2.

“Dipyrromethane” as used herein includes both unsubstituted andsubstituted dipyrromethanes, which may be unsubstituted or substitutedone or more times at the 1, 2, 3, 5, 7, 8 or 9 positions with anysuitable substituent such as halo, carbonyl, alkyl, fluoroalkylincluding perfluoroalkyl, aryl (e.g., A or B at the 5 position;dialkylaminomethyl alkyl at the 1 and 9 positions), Dipyrromethanes maybe coupled to porphyrinic macrocycles at any suitable position on thedipyrromethanes, including the 1, 2, 3, 5, 7, 8, or 9 position, andparticularly the 5 position.

“Metal” as used herein is any suitable metal, including but not limitedto Cu, Zn, Mg, Pt, Pd. Sn, Ni, and Al.

“Metal salt” as used herein includes but is not limited to zinc,palladium, copper, nickel, or cobalt salts. Zinc salts are currentlypreferred. The salts may be formed with any suitable counterion(s),including but not limited to acetate, chloride, acac (acetylacetate),etc.

“Surface attachment group” may be any reactive substituent useful forattaching a compound to a substrate such as a metal, insulator,semiconductor substrate or polymer, which reactive substituent may becoupled directly to the parent molecule or coupled to the parentmolecule by a linker included as a portion of the surface attachmentgroup. When the linker is aromatic the surface attachment group is saidto be aromatic.

“Cross-coupling group” may be any reactive substituent useful forcoupling a compound to another compound such as another porphyrin, as asemiconductor substrate or polymer, which reactive substituent may becoupled directly to the parent molecule or coupled to the parentmolecule by a linker included as a portion of the cross-coupling group.When the linker is aromatic the cross-coupling group is said to bearomatic.

“Bioconjugatable group” may be any reactive substituent or member of aspecific binding pair useful for attaching a compound to another organiccompound such as a protein, peptide, nucleic acid (e.g., DNA, RNA),which reactive substituent or member of a specific binding pair may becoupled directly to the parent molecule or coupled to the parentmolecule by an linker included as a portion of the bioconjugatablegroup. When the linker is aromatic the bioconjugatable group is said tobe aromatic.

“Hydrophilic group” refers to any aromatic or aliphatic group that iswater soluble or enhances the water solubility of the correspondingcompound to which it is coupled. Hydrophilic groups may be coupleddirectly to the parent molecule or coupled to the parent molecule by alinker included as a portion of the hydrophilic group. When the linkeris aromatic the bioconjugatable group is said to be aromatic.

“Linkers” are aromatic or aliphatic groups (which may be substituted orunsubstituted and may optionally contain heteroatoms such as N, O, or S)that are utilized to couple a bioconjugatable group, cross-couplinggroup, surface attachment group, hydrophilic group or the like to theparent molecule. Examples include but are not limited to aryl, alkyl,heteroaryl, heteroalkyl (e.g., oligoethylene glycol), peptide, andpolysaccharide linkers, etc.

The disclosures of all United States Patent references cited herein areto be incorporated by reference herein as if fully set forth.

A. Surface Attachment Groups.

As noted above, compounds of the invention can be substituted with asurface attachment group, which may be in protected or unprotected form.A surface attachment group may be a reactive group coupled directly tothe azolo group, or coupled to the azolo group by means of anintervening linker. Linkers L can be aryl, alkyl, heteroaryl,heteroalkyl (e.g., oligoethylene glycol), peptide, polysaccharide, etc.Examples of surface attachment groups (with the reactive site or groupin unprotected form) include but are not limited to:

4-carboxyphenyl,

carboxymethyl,

2-carboxyethyl,

3-carboxypropyl,

2-(4-carboxyphenyl)ethynyl,

4-(2-(4-carboxyphenyl)ethynyl)phenyl,

4-carboxymethylphenyl,

4-(3-carboxypropyl)phenyl,

4-(2-(4-carboxymethylphenyl)ethynyl)phenyl;

4-hydroxyphenyl,

hydroxymethyl,

2-hydroxyethyl,

3-hydroxypropyl,

2-(4-hydroxyphenyl)ethynyl,

4-(2-(4-hydroxyphenyl)ethynyl)phenyl,

4-hydroxymethylphenyl,

4-(2-hydroxyethyl)phenyl,

4-(3-hydroxypropyl)phenyl,

4-(2-(4-hydroxymethylphenyl)ethynyl)phenyl;

4-mercaptophenyl,

mercaptomethyl,

2-mercaptoethyl,

3-mercaptopropyl,

2-(4-mercaptophenyl)ethynyl,

4-(2-(4-mercaptophenyl)ethynyl)phenyl,

4-mercaptomethylphenyl,

4-(2-mercaptoethyl)phenyl,

4-(3-mercaptopropyl)phenyl,

4-(2-(4-mercaptomethylphenyl)ethynyl)phenyl;

4-selenylphenyl,

selenylmethyl,

2-selenylethyl,

3-selenylpropyl,

2-(4-selenylphenyl)ethynyl,

4-selenylmethylphenyl,

4-(2-selenylethyl)phenyl,

4-(3-selenylpropyl)phenyl,

4-selenylmethylphenyl,

4-(2-(4-selenylphenyl)ethynyl)phenyl;

4-tellurylphenyl,

tellurylmethyl,

2-tellurylethyl,

3-tellurylpropyl,

2-(4-tellurylphenyl)ethynyl,

4-(2-(4-tellurylphenyl)ethynyl)phenyl,

4-tellurylmethylphenyl,

4-(2-tellurylethyl)phenyl,

4-(3-tellurylpropyl)phenyl,

4-(2-(4-tellurylmethylphenyl)ethynyl)phenyl;

4-(dihydroxyphosphoryl)phenyl,

(dihydroxyphosphoryl)methyl,

2-(dihydroxyphosphoryl)ethyl,

3-(dihydroxyphosphoryl)propyl,

2-[4-(dihydroxyphosphoryl)phenyl]ethynyl,

4-[2-[4-(dihydroxyphosphoryl)phenyl]ethynyl]phenyl,

4-[(dihydroxyphosphoryl)methyl]phenyl,

4-[2-(dihydroxyphosphoryl)ethyl]phenyl,

4-[2-[4-(dihydroxyphosphoryl)methylphenyl]ethynyl]phenyl;

4-(hydroxy(mercapto)phosphoryl)phenyl,

(hydroxy(mercapto)phosphoryl)methyl,

2-(hydroxy(mercapto)phosphoryl)ethyl,

3-(hydroxy(mercapto)phosphoryl)propyl,

2-[4-(hydroxy(mercapto)phosphoryl)phenyl]ethynyl,

4-[2-[4-(hydroxy(mercapto)phosphoryl)phenyl]ethynyl]phenyl,

4-[(hydroxy(mercapto)phosphoryl)methyl]phenyl,

4-[2-(hydroxy(mercapto)phosphoryl)ethyl]phenyl,

4-[2-[4-(hydroxy(mercapto)phosphoryl)methylphenyl]ethynyl]phenyl;

4-cyanophenyl,

cyanomethyl,

2-cyanoethyl,

3-cyanopropyl,

2-(4-cyanophenyl)ethynyl,

4-[2-(4-cyanophenyl)ethynyl]phenyl,

4-(cyanomethyl)phenyl,

4-(2-cyanoethyl)phenyl,

4-[2-[4-(cyanomethyl)phenyl]ethynyl]phenyl;

4-cyanobiphenyl;

4-aminophenyl,

aminomethyl,

2-aminoethyl,

3-aminopropyl,

2-(4-aminophenyl)ethynyl,

4-[2-(4-aminophenyl)ethynyl]phenyl,

4-aminobiphenyl;

4-formylphenyl,

4-bromophenyl,

4-iodophenyl,

4-vinylphenyl,

4-ethynylphenyl,

4-allylphenyl,

4-[2-(trimethylsilyl)ethynyl]phenyl,

4-[2-(triisopropylsilyl)ethynyl]phenyl,

4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl;

formyl,

bromo,

iodo,

bromomethyl,

chloromethyl,

ethynyl,

vinyl,

allyl;

4-(ethynyl)biphen-4′-yl,

4-[2-(triisopropylsilyl)ethynyl]biphen-4′-yl,

3,5-diethynylphenyl;

4-(bromomethyl)phenyl, and

2-bromoethyl.

In addition to the monodentate linker-surface attachment groupsdescribed above, multidentate linkers can be employed [Nikitin, K. Chem.Commun. 2003, 282-283; Hu, J.; Mattern, D. L. J. Org. Chem. 2000, 65,2277-2281; Yao, Y.; Tour, J. M. J. Org. Chem. 1999, 64, 1968-1971; Fox,M. A. et al. Langmuir, 1998, 14, 816-820; Galoppini, E.; Guo, W. J. Am.Chem. Soc. 2001, 123, 4342-4343; Deng, X. et al. J. Org. Chem. 2002, 67,5279-5283; Hector Jr., L. G. et al. Surface Science, 2001, 494, 1-20;Whitesell, J. K.; Chang, H. K. Science, 1993, 261, 73-76; Galoppini, E.et al. J. Am. Chem. Soc. 2002, 67, 7801-7811; Siiman, O. et al.Bioconjigate Chem. 2000, 11, 549-556]. Tripodal linkers bearing thiol,carboxylic acid, alcohol, or phosphonic acid units are particularlyattractive for firmly anchoring a molecular device on a planar surface.Specific examples of such linkers are built around the triphenylmethaneor tetraphenylmethane unit, including the following:

1,1,1-tris[4-(S-acetylthiomethyl)phenyl]methyl,

4-{1,1,1-tris[4-(S-acetylthiomethyl)phenyl]methyl}phenyl,

1,1,1-tris[4-(dihydroxyphosphoryl)phenyl]methyl,

4-{1,1,1-tris[4-(dihydroxyphosphoryl)phenyl]methyl }phenyl,

1,1,1-tris[4-dihydroxyphosphorylmethyl)phenyl]methyl, and

4-{1,1,1-tris[4-(dihydroxyphosphorylmethyl)phenyl]methyl }phenyl;

All as described in Balakumar, Muthukumaran and Lindsey, U.S. patentapplication Ser. No. 10/867,512 (filed Jun. 14, 2004). See also Lindsey,Loewe, Muthukumaran, and Ambroise, US Patent Application Publication No.20050096465 (Published May 5, 2005), particularly paragraph 51 thereof.Additional examples of multidentate linkers include but are not limitedto:

-   Alkene surface attachment groups (2, 3, 4 carbons) such as:

3-vinylpenta-1,4-dien-3-yl,

4-(3-vinylpenta-1,4-dien-3-yl)phenyl,

4-(3-vinylpenta-1,4-dien-3-yl)biphen-4′-yl,

4-allylhepta-1,6-dien-4-yl,

4-(4-allylhepta-1,6-dien-4-yl)phenyl,

4-(4-allylhepta-1,6-dien-4-yl)biphen-4′-yl,

5-(1-buten-4-yl)nona-1,8-dien-5-yl,

4-[5-(1-buten-4-yl)nona-1,8-dien-5-yl]phenyl,

4-[5-(1-buten-4-yl)nona-1,8-dien-5-yl]biphen-4′-yl, etc.

-   Alkyne surface attachment groups (2, 3, 4 carbons) such as:

3-ethynylpenta-1,4-diyn-3-yl,

4-(3-ethynylpenta-1,4-diyn-3-yl)phenyl,

4-(3-ethynylpenta-1,4-diyn-3-yl)biphen-4′-yl,

4-propargylhepta-1,6-diyn-4-yl,

4-(4-propargylhepta-1,6-diyn-4-yl)phenyl,

4-(4-propargylhepta-1,6-diyn-4-yl)biphen-4′-yl,

5-(1-butyn-4-yl)nona-1,8-diyn-5-yl,

4-[5-(1-butyn-4-yl)nona-1,8-diyn-5-yl]phenyl,

4-[5-(1-butyn-4-yl)nona-1,8-diyn-5-yl]biphen-4′ -yl,

-   Alcohol surface attachment groups (1, 2, 3 carbons), such as:

2-(hydroxymethyl)-1,3-dihydroxyprop-2-yl,

4-[2-(hydroxymethyl)-1,3-dihydroxyprop-2-yl]phenyl,

4-[2-(hydroxymethyl)-1,3-dihydroxyprop-2-yl]biphen-4′-yl,

3-(2-hydroxyethyl)-1,5-dihydroxypent-3-yl,

4-[3-(2-hydroxyethyl)-1,5-dihydroxypent-3-yl]phenyl,

4-[3-(2-hydroxyethyl)-1,5-dihydroxypent-3-yl]biphen-4′-yl,

4-(3-hydroxypropyl)-1,7-dihydroxyhept-4-yl,

4-[4-(3-hydroxypropyl)-1,7-dihydroxyhept-4-yl]phenyl,

4-[4-(3-hydroxypropyl)-1,7-dihydroxyhept-4-yl]biphen-4′-yl, etc.,

-   Thiol surface attachment groups (1, 2, 3 carbons) such as:

2-(mercaptomethyl)-1,3-dimercaptoprop-2-yl,

4-[2-(mercaptomethyl)-1,3-dimercaptoprop-2-yl]phenyl,

4-[2-(mercaptomethyl)-1,3-dimercaptoprop-2-yl]biphen-4′-yl,

3-(2-mercaptoethyl)-1,5-dimercaptopent-3-yl

4-[3-(2-mercaptoethyl)-1,5-dimercaptopent-3-yl]phenyl,

4-[3-(2-mercaptoethyl)-1,5-dimercaptopent-3-yl]biphen-4′-yl,

4-(3-mercaptopropyl)-1,7-dimercaptohept-4-yl,

4-[4-(3-mercaptopropyl)-1,7-dimercaptohept-4-yl]phenyl,

4-[4-(3-mercaptopropyl)-1,7-dimercaptohept-4-yl]biphen-4′ -yl etc.,

-   Selenyl surface attachment groups (1, 2, 3 carbons), such as:

2-(selenylmethyl)-1,3-diselenylprop-2-yl,

4-[2-(selenylmethyl)-1,3-diselenylprop-2-yl]phenyl,

4-[2-(mercaptomethyl)-1,3-dimercaptoprop-2-yl]biphen-4′-yl,

3-(2-selenylethyl)-1,5-diselenylpent-3-yl,

4-[3-(2-selenylethyl)-1,5-diselenylpent-3-yl]phenyl,

4-[3-(2-selenylethyl)-1,5-diselenylpent-3-yl]biphen-4′-yl,

4-(3-selenylpropyl)-1,7-diselenylhept-4-yl,

4-[4-(3-selenylpropyl)-1,7-diselenylhept-4-yl]phenyl,

4-[4-(3-selenylpropyl)-1,7-diselenylhept-4-yl]biphen-4′-yl, etc.

-   Phosphono surface attachment groups (1, 2, 3 carbons), such as:

2-(phosphonomethyl)-1,3-diphosphonoprop-2-yl,

4-[2-(phosphonomethyl)-1,3-diphosphonoprop-2-yl]phenyl,

4-[2-(phosphonomethyl)-1,3-diphosphonoprop-2-yl]biphen-4′-yl,

3-(2-phosphonoethyl)-1,5-diphosphonopent-3-yl,

4-[3-(2-phosphonoethyl)-1,5-diphosphonopent-3-yl]phenyl,

4-[3-(2-phosphonoethyl)-1,5-diphosphonopent-3-yl]biphen-4′ -yl,

4-(3-phosphonopropyl)-1,7-diphosphonohept-4-yl,

4-[4-(3-phosphonopropyl)-1,7-diphosphonohept-4-yl]phenyl,

4-[4-(3-phosphonopropyl)-1,7-diphosphonohept-4-yl]biphen-4′-yl, etc.,and

-   Carboxylic acid surface attachment groups (1, 2, 3 carbons), such    as:

2-(carboxymethyl)-1,3-dicarboxyprop-2-yl,

4-[2-(carboxymethyl)-1,3-dicarboxyprop-2-yl]phenyl,

4-[2-(carboxymethyl)-1,3-dicarboxyprop-2-yl]biphen-4′-yl,

3-(2-carboxyethyl)-1,5-dicarboxypent-3-yl,

4-[3-(2-carboxyethyl)-1,5-dicarboxypent-3-yl]phenyl,

4-[3-(2-carboxyethyl)-1,5-dicarboxypent-3-yl]biphen-4′-yl,

4-(3-carboxypropyl)-1,7-dicarboxyhept-4-yl,

4-[4-(3-carboxypropyl)-1,7-dicarboxyhept-4-yl]phenyl,

4-[4-(3-carboxypropyl)-1,7-dicarboxyhept-4-yl]biphen-4′-yl, etc.

B. Cross-Coupling Groups.

Compounds produced of the present invention, as individual ring systemsor as constituents of sandwich coordination compounds, can be coupledtogether as linear polymers in like manner as described in U.S. Pat. No.6,777,516 to Li, Gryko and Lindsey. Examples of suitable linking orcross-coupling groups include but are not limited to groups J² and J³below, which may be linked directly to the compound of the invention orby an intervening linker L. Linkers L can be aryl, alkyl, heteroaryl,heteroalkyl (e.g., oligoethylene glycol), peptide, polysaccharide, etc.The cross-coupling group may be simply a reactive attachment group ormoiety (e.g., —R′ where R′ is a reactive group such as bromo), or maycomprise a combination of an intervening linker group coupled to areactive group (e.g., —R″R′, where R′ is a reactive group and R″ is anintervening group such as a hydrophilic group).

Particular examples of linkers include, but are not limited to,4,4′-diphenylethyne, 4,4′-diphenylbutadiyne, 4,4′-biphenyl,1,4-phenylene, 4,4′-stilbene. 1,4-bicyclooctane, 4,4′-azobenzene,4,4′-benzylideneaniline, and 4,4″-terphenyl.

Dyads. The synthesis of dyads of compounds of the invention can proceedvia several different types of reactions. The reactions of interestinclude Glaser (or Eglinton) coupling of two identical porphyrins(generating a butadiyne linker), Cadiot-Chodkiewicz coupling of twoporphyrins (generating a butadiyne linker), Sonogashira coupling of twodifferent porphyrins (generating an ethyne linker), Heck or Wittigreactions of two different porphyrins (generating an alkene linker),Suzuki coupling of two different porphyrins (generating a phenylene orbiphenyl linker), etc. Other reactions can also be employed.

J¹-L-TD-L-J² + J³-L-TD-L-J⁴ J² J³ Reaction Type —B(OH)₂ —Cl, —Br, —ISuzuki

—Cl, —Br, —I Sonogashira

Glaser

Cadiot-Chodkiewicz —CHO —Br, —I Wittig —HC═CH₂ —Br, —I Heck

Polymers. The methods for synthesis of polymeric arrays of compoundsinclude but are not restricted to use of the following types ofreactions:

-   -   Glaser (or Eglinton) coupling of a monomeric porphyrins        (generating a butadiyne linker)    -   Cadiot-Chodkiewicz coupling of two different compounds        (generating a butadiyne linker joining a block copolymer)    -   Sonogashira coupling of two different compounds (generating an        ethyne linker joining a block copolymer)    -   Heck or Witting reactions of two different compounds (generating        an alkene linker joining a block copolymer)    -   Suzuki coupling of two different compounds (generating a        phenylene or biphenyl linker joining a block copolymer)    -   We also can polymerize compounds bearing substituents such as        two or more thiophene groups (generating an oligothiophene        linker) or two or more pyrrole groups (generating a polypyrrole        linker).

The synthesis of the polymers can be performed using stepwise methods orusing polymerization methods. Both methods generally require tworeactive groups attached to the porphyrin in order to prepare a polymerwhere the porphyrins are integral components of the polymer backbone.(An alternative design yields pendant polymers where the porphyrins areattached via one linkage to the polymer backbone.) The stepwisesynthetic method generally requires the use of protecting groups to maskone reactive site, and one cycle of reactions then involves couplingfollowed by deprotection. In the polymerization method no protectinggroups are employed and the polymer is prepared in a one-flask process.

The polymerizations can take place in solution or can be performed withthe polymer growing from a surface. The polymerization can be performedbeginning with a solid support as in solid-phase peptide or DNAsynthesis, then removed. purified, and elaborated further for specificapplications. The polymerization can also be performed with the nascentpolymer attached to an electroactive surface, generating the desiredelectronic material in situ.

C. Bioconjugatable Groups.

Biconjugatable groups may be included in compounds of the invention toprovide a reactive site for conjugation so that the compounds may becoupled to or conjugated to other groups, such as proteins, peptides,targeting agents such as antibodies, polymers, particles such asnanoparticles, organic, polymeric or inorganic beads, other solidsupport surfaces, etc, to form additional active compounds of theinvention. In general each group is attached to a linking groupincluding a linker which can be aryl, alkyl, heteroaryl, heteroalkyl(e.g., oligoethylene glycol), peptide, polysaccharide, etc. The linkinggroup may be simply a reactive attachment group or moiety (e.g., —R′where R′ is a reactive group such as bromo), or may comprise acombination of an intervening group coupled to a reactive group (e.g.,—R″R′, where R′ is a reactive group and R′ is an intervening group suchas a hydrophilic group).

For bioconjugation purposes, the choice of water-solubilizing group(s)and conjugation groups is made so as to achieve orthogonal coupling. Forexample, if a carboxylic acid is used for water solubility, an aldehydemight be used for bioconjugation (via reductive amination with anamino-substituted biomolecule). If a carboxylic acid is used forbioconjugation (via carbodiimide-activation and coupling with anamino-substituted biomolecule), then a complementary group can be usedfor water solubility (e.g., sulfonic acid, guanidium, pyridinium).Bioconjugatable groups include amines (including amine derivatives) suchas isocyanates, isothiocyanates, iodoacetamides, azides, diazoniumsalts, etc. acids or Acid derivatives such as N-hydroxysuccinimideesters (more generally, active esters derived from carboxylic acids;e.g., p-nitrophenyl ester), acid hydrazides, etc., and other linkinggroups such as aldehydes, sulfonyl chlorides, sulfonyl hydrazides,epoxides, hydroxyl groups, thiol groups, maleimides, aziridines,acryloyls, halo groups, biotin, 2-Iminobiotin, etc. Linking groups suchas the foregoing are known and described in U.S. Pat. Nos. 6,728,129;6,657,884; 6,212,093; and 6,208,553.

Conjugates. Other groups can be attached to the compounds of theinvention to form a conjugate by means of a cross-coupling group orbioconjugatable group to tune or adjust the solubility properties of thecompound, including hydrophobic groups, hydrophilic groups, polargroups, or amphipathic groups. The polar groups include carboxylic acid,sulfonic acid, guanidinium, carbohydrate, hydroxy, amino acid,pyridinium, imidazolium, etc. Such groups can be attached tosubstituents that are linear or branched alkyl (e.g., swallowtail),aryl, heteroaryl, heteroalkyl (e.g., oligoethylene glycol), peptide,polysaccharide, etc. Targeting groups such as antibodies, proteins,peptides, and nucleic acid may be attached by means of the linkinggroup. Particles such as nanoparticles, glass beads, etc. may beattached by means of the linking group. Where such additional compoundsare attached to form a conjugate thay may be attached directly to thecompound or attached by means of an intervening group such as ahydrophilic group, depending upon the particular linking group employed(as noted above).

Hydrophilic groups. Compounds of the present invention may includehydrophilic groups coupled thereto as groups A and/or B, e.g.,covalently coupled thereto directly or by an intervening linker, tofacilitate delivery thereof, or improve stability, in accordance withknown techniques. Suitable hydrophilic groups are typically polyols orpolyalkylene oxide groups, including straight and branched-chainpolyols, with particular examples including but not limited topoly(propylene glycol), polyethylene-polypropylene glycol orpoly(ethylene glycol). The hydrophilic groups may have a number averagemolecular weight of 20,000 to 40,000 or 60,000. Suitable hydrophilicgroups and the manner of coupling thereof are known and described in,for example, U.S. Pat. Nos. 4,179,337; 5,681,811; 6,524,570; 6,656,906;6,716,811; and 6,720,306. For example, compounds can be pegylated usinga single 40,000 molecular weight polyethylene glycol moiety that isattached to the compound by means of a linking group.

D. Reactions.

As noted above, the present invention provides a method of making aporphyrin of Formula I:

wherein:

A and B are each independently is selected from the group consisting ofH, alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl,cycloalkylalkenyl, cycloalkylalkynyl, aryl, arylalkyl, arylalkenyl,arylalkynyl, alkoxy, halo, mercapto, azido, cyano, hydroxyl, nitro,acyl, alkoxy, alkylthio, amino, alkylamino, arylalkylamino,disubstituted amino, acylamino, acyloxy, amide, sulfonamide, urea,alkoxylacylamino, aminoacyloxy, hydrophilic groups, surface attachmentgroups, cross-coupling groups and bioconjugatable groups (with Apreferably aryl, including aromatic hydrophilic groups, aromatic surfaceattachment groups, aromatic cross-coupling groups, and aromaticbioconjugatable groups);

R¹ is selected from the group consisting of H, alkyl and aryl(preferably H);

R², R³, R⁴, R⁵, R⁷, R⁸, R⁹, and R¹⁰ are each independently selected fromthe group consisting of H, halo, loweralkoxy, and loweralkylthio; and

M is a metal or a pair of hydrogen atoms;

said method comprising:

(a) condensing (i) a bis(imino)dipyrromethane of Formula II:

wherein:

R is alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl,cycloalkylalkenyl, cycloalkylalkynyl, aryl, arylalkyl, arylalkenyl,arylalkynyl, alkoxy, or acyl; and

A, R¹, R², R³, R⁴, and R⁵ are as given above, with (ii) a dipyrromethaneof Formula III:

wherein B, R⁷, R⁸, R⁹ and R¹⁰ are as given above, in a polar ornonpolar, protic or aprotic organic solvent containing a metal salt toproduce a reaction product; then (b) optionally oxidizing said reactionproduct with an oxidizing agent; and then (c) optionally demetallatingsaid reaction product to produce the porphyrin of Formula I. Thereaction conditions are not critical and any suitable solvent can beused, including but not limited to methanol, ethanol, propanol,isopropanol, chloroform. tetrahydrofuran, dichloromethane, toluene, andmixtures thereof. The reaction can be carried out at any convenienttemperature such as between 0 and 100° C. Any suitable metal salt can beused, including but not limited to zinc, palladium, copper, nickel andcobalt salts (which then provides the metal M for the compound ofFormula I). For some substituents no external oxidizing agent isrequired and oxidation is achieved by oxygen in ambient air. When anoxidizing agent is required any suitable oxidizing agent can be used,such as oxygen or a quinone oxidizing agent such asdichlorodicyanobenzoquinone (DDQ), p-chloranil, and o-chloranil. Thedemetallating step can be carried out in accordance with knowntechniques by treating or mixing the metallated compound with anysuitable acid (e.g., acetic acid, trifluoroacetic acid, hydrochloricacid, sulfuric acid, etc.).

In some embodiments A is preferably an aromatic, or aryl, group,including aromatic hydrophilic groups, aromatic surface attachmentgroups, aromatic cross-coupling groups, or aromatic bioconjugatablegroup (for example, an aryl-containing linker group substituted one ormore timeswith an alkene, alkyne, alcohol, thiol, selenyl, phosphono,carboxylic acid, formyl, halo or amine group).

In some embodiments, B is preferably a hydrophilic group, surfaceattachment group, cross-coupling group, or bioconjugatable group (e.g.,an alkene, alkyne, alcohol, thiol, selenyl, phosphono, carboxylic acid,formyl, halo or amine group, coupled directly to the parent molecule orby means of an intervening linker group).

In some embodiments, A is a bioconjugatable group and B is a hydrophilicgroup as given above; or A is a hydrophilic group and B is abiconjugatable group as given above.

The present invention also provides a method of making a compound ofFormula II:

wherein:

R, is alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl,cycloalkylalkenyl, cycloalkylalkynyl, aryl, arylalkyl, arylalkenyl,arylalkynyl, alkoxy, or acyl;

R¹ is H, alkyl or aryl, preferably H;

R², R³, R⁴, and R⁵ are each independently selected from the groupconsisting of H, halo, loweralkoxy, and loweralkylthio; and

A is as given above, preferably aryl.

The method comprises reacting a dipyrromethane of Formula IV:

wherein A, R¹, R², R³, R⁴ and R⁵ are as given above, with a compound ofFormula V:R—NH₂  (V)wherein R is as given above in an organic solvent to produce saidcompound of Formula II. The reaction conditions are not critical and canbe carried out in any suitable organic solvent (such as describedabove), neat if desired, at any convenient temperature such as 0 to 100°C. The compound of Formula V is preferably included in a stoichiometricamount, preferably in excess, for example five, ten or twenty timesexcess. Suitable solvents include but are not limited to methylenechloride, chloroform, tetrahydrofuran, nitromethane, toluene,acetonitrile, methanol, ethanol, and mixtures thereof.

Compounds of Formula IV and Formula V can be made in accordance withknown techniques for the synthesis of dipyrromethanes and amines, orvariations thereof that will be apparent to persons skilled in the art.

E. Utility.

Porphyrins produced by the methods and intermediates described hereinare useful, among other things, for the production of polymers thereofwhich may be immobilized or coupled to a substrate and used as lightharvesting rods, light harvesting arrays, and solar cells, as describedfor example in U.S. Pat. No. 6,407,330 to Lindsey et al. or U.S. Pat.No. 6,420,648 to Lindsey. Compounds produced by the methods andintermediates of the invention are also useful immobilized to asubstrate for making charge storage molecules and information storagedevices containing the same. Such charge storage molecules andinformation storage devices are known and described in, for example,U.S. Pat. No. 6,208,553 to Gryko et al.; U.S. Pat. No. 6,381,169 toBocian et al.; and U.S. Pat. No. 6,324,091 to Gryko et al. The compoundscan be coupled to substrates to form molecular batteries, molecularcapacitors and electrochromic displays as described in U.S. Pat. No.6,777,516 to Li et al. The porphyrin may comprise a member of a sandwichcoordination compound in the information storage molecule, such asdescribed in U.S. Pat. No. 6,212,093 to Li et al., U.S. Pat. No.6,451,942 to Li et al., or U.S. Pat. No. 6,777,516 to Li et al.

Porphyrins produced by the methods of the invention are useful per se orin further modified form (e.g., as a salt, metalated compound, conjugateor prodrug) for diagnostic and therapeutic purposes in like manner asother compounds described for photodynamic therapy, such as described inUS Patent Application Publication No. 2004/0044197 to Pandey et al.

The present invention is explained in greater detail in the followingnon-limiting Examples.

EXAMPLES

Imine groups have been briefly described as C₁ synthons for thesynthesis of A₄-porphyrins by the condensation of an aldimine withpyrrole [23]. Bis(imino)dipyrromethane derivatives are readily availablefrom the corresponding diformyldipyrromethane by imination with amines[24], and have been used as precursors for expanded porphyrins [25] oras pyrrole-based ligands in metal-directed self-assembly processes [24,26]. However, bis(imino)dipyrromethanes have not been used for thesynthesis of porphyrins as described herein.

Part I below describes synthesis, including the preparation ofbis(imino)dipyrromethanes, development of thedipyrromethane+bis(imino)dipyrromethane condensation, and preparation ofa set of trans-AB-porphyrins. Part II below describes observations andstudies concerning the course of the reaction and intermediates formedwith the bis(imino)dipyrromethanes.

Part I. Synthesis

Synthesis of 5-substituted dipyrromethanes. Dipyrromethanes 1a-1 havebeen prepared previously by a variety of procedures [1, 21, 22, 27-33].A one-flask solventless synthesis of meso-substituted dipyrromethanesenables direct purification by recrystallization (withoutaqueous/organic extraction, chromatography, or distillation) [34].Following this procedure, condensation of the desired aldehyde(paraformaldehyde, in case of 1j) and pyrrole (100 equiv) at roomtemperature using InCl₃ (MgBr₂ for 1c) followed by recrystallizationafforded multi-gram quantities of the desired meso-substituteddipyrromethanes 1a-1 in yields of 14-88% (Chart 1). Dipyrromethane 1kwas prepared by a reported procedure [21]. Dipyrromethanes 1g, 1h, 1i,and 1l were purified by chromatography. The purity of eachdipyrromethane was >97% as determined by GC-FID analysis.

Synthesis of 1,9-diformyldipyrromethanes. Vilsmeier formylation [35] isan established method for preparing 1,9-diformyldipyrromethanes. Adiacyldipyrromethane-tin complexation strategy facilitates isolation andpurification of the 1,9-diacyldipyrromethane, which otherwise are poorlycrystalline and chromatograph with difficulty [36]. Thus, Vilsmeierformylation of dipyrromethanes (1a, 1c, 1d, 1f, 1h) followed bytreatment with TEA and n-Bu₂SnCl₂ in CH₂Cl₂ afforded the crudedibutyltin complex. Purification by filtration through a pad of silicafollowed by treatment with diethyl ether/methanol afforded thedibutyltin complexes as pink solids in 46-67% yield (dibutyltin complexBu₂Sn-2h was obtained as a brown viscous liquid, Table 1). Our attemptsto remove the color by further purification (column chromatography,repeated recrystallization, treatment with activated carbon) provedunsuccessful. However, elemental analysis of each tin complexcorresponded well with the calculated value.

CHART 1 1a-I

R a

b

c

d

e

f

g

h

i

j

k

lDecomplexation with TFA furnished the corresponding1,9-diformyldipyrromethanes (2a [12], 2d [14], 2f) as off-white solids,and 2h was obtained as a brown viscous liquid in 72-86% yields. Theoverall yield of 1,9-diformylation was 30-46%. The separation of 2c andthe tin byproduct from the reaction mixture proved difficult; therefore,2c was used for further reaction without demetalation (vide infra).1,9-Diformyl-5-(pentafluorophenyl)dipyrromethane (2e),1,9-diformyl-5-methydipyrromethane (2g),1,9-diformyl-5-(tridec-7-yl)dipyrromethane (2i), and1,9-diformyldipyrromethane (2j) [37] were purified without using thetin-complexation method.

Synthesis of 1,9-Bis(imino)dipyrromethanes with diverse iminosubstituents. 1,9-Diformyldipyrromethane 2a was condensed with a set ofamines to give the corresponding 1,9-bis(imino)dipyrromethanes assummarized in Table 2. ¹H NMR spectroscopy enabled determination of theratio of diformyldipyrromethane 2a:formyl-iminodipyrromethane:bis(imino)dipyrromethane in the reactionmixture by using the peak from the 5-position proton of dipyrromethanespecies (e.g., 2a, 5.20 ppm; mono-imino species, 5.27 ppm; 3a-Ph, 5.32ppm).

TABLE 1 Synthesis of 1,9-diformyldipyrromethanes

Yield (%)^(b) tin-complexation direct method Entry R method step 1 step2 total 1 a

NA^(c) 58 79 46 2 b

NA 67 —^(d) —^(d) 3 d

NA 53 82 38 4 e

85 NA NA NA 5 f

NA 46 86 40 6 g

78 NA NA NA 7 h

72 42 72 30 8 i

47 NA NA NA 9 j

70 NA NA NA ^(a) Reaction conditions: (a) DMF, POCl₃, at roomtemperature for 1 h; (b) Bu₂SnCl₂ (1 equiv) and triethylamine (3 equiv)in CH₂Cl₂ at room temperature for 20 min to 1 h; (c) TFA in CH₂Cl₂ atroom temperature for 10 min. ^(b) Isolated yield. ^(c) Not attempted.^(d) Not successful; see text.

TABLE 2

Reaction conditions for imine formation with different amines^(a) equiv% Yield^(b) Entry R of amine Temp. Time (h) 2a Monoimine Bis(imine)  1n-Pr- 2.1 rt 24 0 3 97 (3a)  2 n-Pr- 20 rt 1 0 0 100 (3a)  3 PhCH₂— 2.1rt 2 Trace <5 >95 (3a-Bz)  4 p-anisyl- 2.1 rt 1 0 18 82 (3a-An)  5p-anisyl- 2.1 reflux 1 0 6 94 (3a-An)  6 Ph- 2.1 reflux 20 0 19 81(3a-Ph)  7 Ph- 20 rt 1 0 9 91 (3a-Ph)  8^(c) Ph- 20 rt 1 0 Trace >99(3a-Ph)  9 C₆F₅— 2.1 reflux 24 60 40 0 (3a-C₆F₅) 10 C₆F₅— 20 reflux 2410 53 37 (3a-C₆F₅) 11^(d) C₆F₅— 2 rt 0.5 23 57 20 (3a-C₆F₅) ^(a)Reactionconditions: The amine was added to a THF solution of 2a (300 mM).^(b)The yields of imine were assessed by ¹H NMR spectroscopy.^(c)Aniline was used as a solvent. ^(d)TFA (2 equiv) was included.The reaction of 2a and n-propylamine proceeded smoothly at roomtemperature, affording bis(imine) 3a quantitatively (Entry 1). A simplemethod to obtain analytically pure bis(imine) 3a entailed stirringdiformyldipyrromethane 2a and excess n-propylamine for 1 h at roomtemperature, followed by removal of excess n-propylamine (bp=48° C.) invacuto (Entry 2). The resulting bis(imine) 3a could be used forporphyrin formation without further purification. Benzylamine reactedsimilarly with 2a, affording 3a-Bz (Entry 3). p-Anisidine or anilinereacted with diformyldipyrromethane 2a to give bis(imine) 3a-An or 3a-Ph(Entries 4-8), though reaction was facilitated with heating or excessamine. The synthesis of bis(imine) 3a-C₆F₅ required the use of TFA as acatalyst and resulted in recovery of the starting diformyldipyrromethane2a (Entries 9-11). The separation of 3a-C₆F5 by chromatography was notsuccessful. In summary, the reactivity of amines parallels theirsolution basicity:n-propylamine˜benzylamine>p-anisidine>aniline>>2,3,4,5,6-pentafluoroaniline.

Optimization of reaction conditions for porphyrin formation via1,9-bis(imino)dipyrromethanes. The [2+2] condensation of a1,9-bis(imino)dipyrromethane+a dipyrromethane was optimized with respectto imine substituent, reagents, solvent, concentration, and time. Toscreen a large number of different reaction conditions,porphyrin-forming reactions were performed on a small scale. The yieldsof porphyrin were calculated using absorption spectroscopy by removingsmall aliquots from the reaction mixture, assuming ε_(Soret)=500,000 M⁻¹cm⁻¹. The spectroscopic yields and isolated yields corresponded well(vide infra). Samples from the crude reaction mixture were examined bylaser-desorption mass spectrometry (LD-MS) [38] to assess the level ofscrambling [39]. The extent of scrambling was categorized as Level 0 (nodetectable scrambling) to Level 4 (complete scrambling) as describedpreviously [39].

(i) Imine substituents. The effects of N-imino substituents on porphyrinformation were examined by carrying out the reaction of 1b+3a, 3a-Ph,3a-An, or 3a-Bz (Table 3). The reaction with 3a or 3a-Bz affordedporphyrin Zn4ab in yield of up to 40% without use of DDQ. The reactionproceeded in higher yield at reflux versus room temperature. Noporphyrin byproducts (i.e., scrambling) were observed (Entries 1-4). Thereaction of 3a-Ph also proceeded without detectable scrambling, but DDQwas required as an oxidant (Entries 5 and 6). On the other hand, thereaction of 3a-An+1b required DDQ and afforded porphyrin with theformation of scrambled byproducts (Entries 7 and 8). Thus, oxidation wasachieved aerobically with the alkylimino substituents whereas DDQ wasnecessary with arylimino substituents.

TABLE 3 Effects of N-imine substituents in formation of porphyrinZn4ab^(a)

Entry substrate Temp. Yield (%)^(b) Scrambling DDQ 1 3a rt 8 Level 0 — 23a reflux 41 (35^(c)) Level 0 — 3 3a-Bz rt 19 Level 0 — 4 3a-Bz reflux34 Level 0 — 5 3a-Ph rt 6 Level 0 required 6 3a-Ph reflux 40 Level 0required 7 3a-An rt <1 — required 8 3a-An reflux 12 Level 2 required^(a)Reaction conditions; [3a, 3a-Ph, 3a-An, 3a-Bz] and [1b] = 10 mM,Zn(OAc)₂ (10 equiv) in EtOH at room temperature (20 h) or under reflux(18 h), then treated with 3 mol equiv of DDQ (for 3a-Ph and 3a-An;Entries 3-6). ^(b)The yields of porphyrin were determined usingabsorption spectroscopy. ^(c)Isolated yield.

The straightforward synthesis and purification of 3a prompted us to usethe propyl group as an imino substituent for further studies. Tounderstand the robustness of the reaction conditions, the effects ofreagents, solvent, concentration, and time were investigated using thereaction of 3a+1b as a standard. The results are as follows(spectroscopic yields):

(ii) Solvent. Seven solvents of diverse polarity and composition wereexamined (Table 4). Porphyrin was formed in each solvent withoutdetectable scrambling. The highest yield (44%) was obtained in EtOH.

TABLE 4 Effect of solvent in formation of porphyrin Zn4ab^(a)

Yield (%)^(b) Entry Solvent room temperature reflux 1 Toluene 6 41 2CH₂Cl₂ 10 36 3 CHCl₃ 4 37 4 THE 1 9 5 EtOH 9 44 6 MeOH 9 27 7 CH₃CN 2 27^(a)Reaction conditions; [3a] and [1b] = 10 mM, Zn(OAc)₂ (10 equiv) ineach solvent at room temperature (20 h) or under reflux (5 h). ^(b)Theyields of porphyrin were determined using absorption spectroscopy. Noscrambling was observed in each reaction (LD-MS analysis).

(iii) Reagents. The highest yield of porphyrin was obtained when 10equiv of Zn(OAc)₂ was used. The yield was 10% when a stoichiometricamount of Zn(OAc)₂ was used. Other metal reagents [Cu(OAc)₂, Pd(OAc)₂,MgBr₂, or Yb(OTf)₃] in place of Zn(OAc)₂ resulted in a low or negligibleyield of porphyrinic species. Attempts to use a Brønsted acid (TFA oracetic acid) to facilitate reaction at room temperature did not affordporphyrin.

(iv) Temperature.

The reaction at room temperature gave the porphyrin in 8% yield (16-24h) versus ˜40% upon reflux (Table 4).

(v) Concentration. The effects of reactant concentration were examinedover the range from 1 mM to 316 mM. The amount of Zn(OAc)₂ was changedcommensurably with reactant concentration. The highest yield (˜41%spectroscopic yield) was obtained at 10 mM and 31.6 mM (FIG. 1-A). Theyield declined to 28% at the highest concentration examined (316 mM).The lack of a precipitous decline at high concentration indicates theapplicability of this method for large-scale synthetic applications.

(vi) Reaction time. The yield of porphyrin as a function of time with31.6 mM reactants is shown in FIG. 1-B. The formation of porphyrin Zn4abis essentially complete within 1 h.

(vii) Aeration. Small-scale reactions were carried out in a closedvessel containing sufficient headspace to provide more than astoichiometric quantity of air for the oxidation. Large-scale reactionswere carried out with gentle aeration of the reaction vessel such thatsignificant evaporation of the solvent was not observed. Porphyrinformation was complete within 5 h.

On the basis of these studies, the best conditions for porphyrinformation were identified as follows: [3a] and [1b] =10 or 31.6 mM withZn(OAc)₂ (100 mM or 316 mM) in EtOH under reflux exposed to air (orgentle aeration) for 5-24 h. The reaction mixture was quite clean andthe porphyrin was readily purified. Examination of the crude reactionmixture by LD-MS did not show the presence of any other porphyrinspecies.

Exploration of scope

(i) Survey of diverse trans-AB-porphyrins. The optimized conditions wereapplied to the synthesis of various porphyrins (Scheme 3, Table 5).Emphasis was placed on (1) variation of the substituents, (2) assessmentof any scrambling processes, and (3) yields of porphyrin. Altogether,the preparation of 28 trans-AB-porphyrins, 8 trans-A₂-porphyrins, and 8A-porphyrins was examined. The 1,9-bis(imino)dipyrromethanes (3a, 3c-j)were easily prepared as described above and readily characterized by ¹HNMR spectroscopy. The imination was insensitive to the nature of the5-substituents of 1,9-diformyldipyrromethanes and was typically completewithin 30 min.

TABLE 5 Survey of the formation of trans-AB-, A2—, and A-porphyrins^(a)3a 3c 3d 3e

1a

42 26 32 33 1c

36 iS 26 21 1d

30 22 32 26 1e

23 13 25 15 1f

35 24 31 25 1g methyl 30 28 30 30 1h n-pentyl 33 24 31 28 1i

25 19 19 20 1j H 31 27 30 28 3f 3g 3h 3i 3j

CH₃ n-pentyl

H 1a

39 1 0 2 0 1c

27 <1 0 3 0 1d

30 <1 0 1 0 1e

20 <1 0 1 <1 1f

29 <1 0 2 0 1g methyl 32 <1 0 2 1 1h n-pentyl 30 <1 0 2 1 1i

23 <1 0 2 <1 1j H 30 1 <1 1 2 ^(a)The yields of porphyrin weredetermined by absorption spectroscopy of small aliquots from thereaction mixture. All reactions with yields >5% gave level 0 scrambling(detected by LD-MS analysis); scrambling could not be assessed reliablyfor the low-yielding reactions exhibited by 3g-j. Reaction conditions:10 mM reactants and 10 equiv of Zn(OAc)₂ in EtOH under reflux exposed toair for 2 h.

In each case, a mixture of dipyrromethane and1,9-bis(imino)dipyrromethane was treated with Zn(OAc)₂ (10 equiv) inethanol, with concentrations of [3]=[1]=10.0 mM. The reaction mixturewas refluxed for 2 h. The yields of porphyrin were determinedspectroscopically and ranged from <1% to 42% depending on thesubstituents and combination of the dipyrromethane precursors. Eachcrude reaction mixture was examined for the presence of scrambledporphyrin species and none was detected. Note that a given porphyrin canbe made in two ways by switching the combination of the1,9-bis(imino)dipyrromethane (3) and dipyrromethane (1). Regardless ofthe combination, the resulting porphyrinogen should be identical; thus,differences in porphyrin yields should reflect reactivity during thecondensation rather than oxidation (vide infra).

The 1,9-bis(imino)dipyrromethanes substituted with an aromatic group atthe 5-position (3a, 3c-f) reacted with dipyrromethanes having an aryl,alkyl, or no substituent at the 5-position, affording the respectiveporphyrin in 13-42% yield. Porphyrin formation proceeded well regardlessof the presence of electron-donating groups (4-methoxyphenyl, 1d or 3d)or electron withdrawing groups (pentafluorophenyl, 1e or 3e) in eitherthe dipyrromethane or the 1,9-bis(imino)dipyrromethane unit.

To our surprise, attempts to use the 1,9-bis(imino)dipyrromethanes 3g-i(meso-alkyl) and 3j (meso-H) in reactions with dipyrromethanes resultedat best in only a trace of porphyrin. Spectral examination of the crudemixture showed the formation of a zinc complex of the1,9-bis(imino)dipyrromethane as well as the presence of the unreacteddipyrromethane (See Part II). Attempts were made to improve the yield ofthe alkyl/alkyl substituted trans-AB-porphyrins exemplified for thereaction of 3h+1a by examination of diverse reaction conditions. (1)Acid catalysis: Attempts to use a Brønsted acid (TFA or acetic acid) didnot afford porphyrin. (2) Solvent: Replacement of ethanol (bp 78° C.)with 1-butanol (bp 116-118° C.) or 1-pentanol (bp 136-138° C.) underrefluxing conditions gave no change in the yield of porphyrin. Use ofsolvents of diverse polarity and composition (listed in Table 4) did notimprove the yield of porphyrin. Note that 1,9-bis(imino)dipyrromethaneswere readily soluble in ethanol regardless of the nature of the5-substituent; thus, the solubility of 1,9-bis(imino)dipyrromethanes isnot a source of the poor reactivity. (3) Oxidant: Attempts to oxidizethe reaction mixture with DDQ or p-chloranil gave no porphyrin,suggesting the failure originated in the condensation yieldingporphyrinogen rather than the oxidation of the porphyrinogen.

In short, the bis(imino)dipyrromethane+dipyrromethane method is notsuitable for the synthesis of alkyl/alkyl substitutedtrans-AB-porphyrins or alkyl substituted A-porphyrins. By contrast,porphyrin formation proceeded smoothly (19-32%) when the same meso-H andmeso-pentyl substituents were attached to the dipyrromethane unit and anaryl substituent was present at the 5-position of thebis(imino)dipyrromethane.

(ii) Direct synthesis of porphyrins from1,9-bis(imino)dipyrromethane-tin complexes. A streamlined synthesis wasexamined by direct imination of the 1,9-diformyldipyrromethane-tincomplex, thereby avoiding the TFA-induced decomplexation step (Scheme4). The reaction of tin complex Bu₂Sn-2a and n-propylamine proceededsmoothly at room temperature over 2 h to give 3a in quantitative yield.This direct imination method may be useful in cases where exposure toBrønsted acids needs to be minimized. The formation of thebis(imino)dipyrromethane species was readily assessed by ¹H NMRspectroscopy, monitoring the disappearance and appearance of theresonances due to the aldehyde (9.14 ppm) and imino (7.95 ppm) groups,respectively, over the course of 2 h. After imination, the crude sampleof 3a was reacted with 1b, affording Zn4ab in 30% spectroscopic yield.The yield was slightly lower than that with the imination of theuncomplexed diformyldipyrromethane (37%); however, the lower yield isoffset by the omission of one step in the sequence. The dibutyltinbyproducts present in the crude reaction mixture after imination havelittle consequence on porphyrin formation other than the minor decreasein yield.

This approach was applied with Bu₂Sn-2c. The reaction of tin complexBu₂Sn-2c and n-propylamine proceeded smoothly at room temperature and 3cwas obtained quantitatively as evidenced by ¹H NMR spectroscopy. Theresulting crude sample of 3c was reacted with dipyrromethanes 1a,c-j toform the corresponding zinc porphyrins in yields of 19-32% (Table 5).

(iii) Preparative synthesis of porphyrins. A series of trans-AB-,trans-A₂-, and A-porphyrins bearing diverse substituents was preparedand isolated (Table 6). In each case, examination of the crude reactionmixture showed no detectable scrambling. Each porphyrin was purified ina straightforward manner by passage over a short pad of silica. Theisolated yields (30-38%) of the trans-AB-porphyrins are comparable tothe spectroscopic yields (Table 5, 35-42%). To establish a benchmark forcomparison with reactions of bis(imino)dipyrromethanes versusdiformyldipyrromethanes, the condensation of 1,9-diformyldipyrromethane2a+the dipyrromethane 1b was examined, which affordedtrans-AB-porphyrins Zn4ab in 6% yield (Entry 2). The synthesis ofporphyrins by reaction of a 1,9-diformyldipyrromethane+a dipyrromethanein the presence of p-toluenesulfonic acid and zinc acetate also has beendescribed [8].

Aerobic oxidation. The observation that porphyrin formation can beachieved aerobically (without use of a quinone oxidant such as DDQ orp-chloranil) is somewhat surprising. Typically, the direct aerobicoxidation of porphyrinogens only can be achieved at high temperature[40]. Oxidation at more modest temperatures (including room temperature)can be achieved aerobically in the presence of oxygen-activationcatalysts [41], or anaerobically with quinone oxidants [42]. The keydifference here is that the porphyrinogen formed from reaction of abis(imino)dipyrromethane+dipyrromethane is expected to bear analkylamino group at each of the 5- and 15-positions, rather than moretypical hydrocarbon substituents.

TABLE 6 Synthesis of trans-AB, trans-A₂, and A-porphyrins^(a) YieldEntry R¹ R² Porphyrin (Type) (%)^(b) 1 3a

1b

Zn4ab (AB) 37 2 2a (diformyl species)

1b

Zn4ab (AB) 6 3 3d

1e

Zn4de (AB) 30 4 3e

1d

Zn4de (AB) 32 5 3f

1k

Zn4fk (AB) 38 6 3a

1a

Zn4aa (A₂) 36 7 3c

1j

Zn4cj (A) 38 8 3a

1h

Zn4ah (AB) 32 ^(a)Reactions were performed at 0.1-0.5 mmol scale.Reaction conditions: [3] and [1] = 31.6 mM ([2] and [1] = 10 mM forEntry 2), Zn(OAc)₂ (10 equiv) in refluxing ethanol exposed to air (18h). All reactions give level 0 scrambling (assessed by LD-MS analysis).^(b)Isolated yields.The putative 5,15-bis(alkylamino)porphyrinogen is shown in Scheme 5 forthe reaction of the free-base precursors dipyrromethane 1 andbis(imino)dipyrromethane 3. Elimination of the amines (loss of 2 RNH₂)transforms the porphyrinogen (a hexahydroporphyrin) to adihydroporphyrin. The latter apparently undergoes facile oxidation with½O₂ to give the porphyrin with formation of one equivalent of H₂O. Zincinsertion may occur upon formation of the free base porphyrin or at anearlier stage in the process. Although this picture provides a partialexplanation of the observed results, further studies are required toidentify why aliphatic amines afford conversion without a quinoneoxidant while those with aniline are less inclined toward thisconversion. One possibility is that the greater basicity of thealiphatic amines versus aromatic amines facilitates complexation orprotonation, in turn yielding a better leaving group.

Part II. Reaction course. We made a number of observations concerningthe conversion of a bis(imino)dipyrromethane+a dipyrromethane to theporphyrin. Two key observations were as follows: (1) For alkyl orH-substituted bis(imino)dipyrromethanes, which did not affordporphyrins, peaks in the higher mass region were observed (m/z=692.3 forH-substituted 3j; m/z=832.6 for pentyl-substituted 3l). (2) The crudereaction mixture of a porphyrin-forming reaction exhibits the peakexpected for the zinc porphyrin (e.g., m/z=538.5 for Zn4ab, derived from3a+1b), and, when the reaction is performed at higher concentration, asimilar unexpected set of peaks at higher mass (m/z=844.0). Upon workup,the isolated porphyrin gave only the expected molecule ion peak.

A lengthy study was performed to understand whether the observed resultscould explain the disparate reactivity of the aryl- versus alkyl- orH-substituted bis(imino)dipyrromethanes. A framework for presentation ofthe results is provided in FIG. 2. The key results from the studies areas follows:

(1) The bis(imino)dipyrromethane reacts rapidly with zinc acetate togive a dimer composed of two bis(imino)dipyrromethanes and two zincatoms, (3)₂Zn₂, which accounts for the unexpected peaks in the massspectrum.

(2) The dimer (3)₂Zn₂ forms reversibly, regardless of the nature of themeso substituent (aryl, alkyl, H), and undergoes facile disassembly uponexposure to water or trace acid. The complex derived from a5-aryl-substituted bis(imino)dipyrromethane, e.g., (3a)₂Zn₂, reacts witha dipyrromethane, either directly or via the uncomplexed species 3a, togive the porphyrin.

(3) ¹H NMR examination of the crude reaction mixture with analkyl-substituted bis(imino)dipyrromethane (3g) revealed that thedipyrromethane counterpart (1a) remained intact and unreacted.

(4) The pale orange solution of a bis(imino)dipyrromethane (3) bearingan aryl (but not alkyl or H) substituent slowly turns purple uponstanding overnight. The color change stems from the conversion ofaryl-substituted bis(imino)dipyrromethane to the corresponding dipyrrin(e.g., 3a→5a). The bis(imino)dipyrromethane complex with zinc, (3a)₂Zn₂,can undergo oxidation to the corresponding bis[bis(imino)dipyrrin]zinccomple, (5a)₂Zn, which does not react with a dipyrromethane to give theporphyrin.

The key studies that led to these results are summarized below, andadditional information is provided in the Experimental Section.

Formation of (3a)₂Zn₂. Bis(imino)dipyrromethane 3a was treated withZn(OAc)₂ in ethanol at room temperature in the absence of adipyrromethane. The reaction was followed by absorption spectroscopy, ¹HNMR spectroscopy, and LD-MS analysis. The vivid pink mixture formedimmediately gave an unexpected peak at m/z=844.0, which is assigned tothe complex composed of two bis(imino)dipyrromethanes and two zincatoms: (3a)₂Zn₂. The formation of (3a)₂Zn₂ was essentially completewithin 1 min at room temperature as shown by absorption spectroscopy(FIG. 3). The absence of a peak in the ˜450-520 nm region characteristicof dipyrrin species [43] indicates that (3a)₂Zn₂ contains thedipyrromethane, not dipyrrin, framework. In general, each of thebis(imino)dipyrromethanes that was examined (3a, 3j, 3l) was observed toform the corresponding (3)₂Zn₂ complex.

Formation of (5a)₂Zn. On standing for a prolonged period (18 h), at roomtemperature, the initial pink mixture containing (3a)₂Zn₂ slowly turneddeep purple owing to the formation of (5a)₂Zn. The purple color stemsfrom the appearance of a new absorption band at 545 nm characteristic ofbis(dipyrrinato)Zn(II) complexes. LD-MS analysis gave a new peak atm/z=777.4 (consistent with a complex derived from two molecules ofbis(imino)dipyrrin 5a and one zinc atom: 778.3 Da). The conversion of(3a)₂Zn₂ to bis(dipyrrinato)Zn(II) complex (5a)₂Zn was more pronouncedwhen the reaction of 3a+Zn(OAc)₂ (which quantitatively gave (3a)₂Zn₂ in1 min) was carried out under reflux (FIG. 3B). After 2 h, the absorptionband corresponding to (3a)₂Zn₂ had disappeared. Also, the conversion of(3a)₂Zn₂ to (5a)₂Zn is not entirely clean: upon refluxing (3a)₂Zn₂ inEtOH (31.6 mM) in air for 2 days, (5a)₂Zn was formed in >50% (but notquantitative) yield owing to the concomitant formation of high molecularweight material.

It is noteworthy that similar treatment of complex (3j)₂Zn₂ did not givean oxidized species analogous to (5j)₂Zn. These observations show acorrelation between the ease of oxidation of (3)₂Zn₂ and the ease offormation of the porphyrin from this complex. Why this should be thecase remains unclear.

Structure of complexes (3)₂Zn₂. The proposed structure for (3a)₂Zn₂ ishelical wherein each zinc atom is bonded to two pyrrolic nitrogen atoms(on distinct dipyrromethanes) and coordinated to the N_(imino) atoms(not shown). Analogous helical dipyrromethane-metal complexes containingMn(II) and Fe(II) have been reported, wherein the dipyrromethane bears ageminal dimethyl group at the meso position [26]. Related to thesestructures are the “accordion-porphyrins,” which contain twobis(imino)dipyrromethanes, each of which is singly metal-coordinated andheld apart from the other by α,ω-diaminoalkyl groups spanning the iminemoieties [25]. Molecular modeling of (3a)₂Zn₂ shows that thezinc-N_(pyrrole) distance (1.95 Å) and the zinc-N_(imine) distance (2.19Å) match well with those of known pyrrole-imine zinc complexes (1.93 Åand 2.16 Å) [44]. No discernible differences in conformation wereobserved owing to the nature of the meso substituent (aryl, alkyl, H).

Reactivity of complexes (3a)₂Zn₂ and (5a)₂Zn. To determine whethercomplexes (3a)₂Zn₂ and (5a)₂Zn were intermediates along the path toporphyrin or unreactive side products, the order-of-addition ofreactants was examined. In the standard reaction, an ethanol solution ofbis(imino)dipyrromethane 3a and dipyrromethane 1b is treated withZn(OAc)₂, followed by reflux exposed to air for 2 h, whereupon porphyrinis obtained in ˜40% yield (Table 7, Entry 1). Three experiments wereperformed:

(1) A mixture of dipyrromethane 1b was treated with Zn(OAc)₂ at roomtemperature for 30 min before adding bis(imino)dipyrromethane 3a, andthen refluxing for 2 h (Entry 2). Porphyrin was obtained in yieldcomparable to that of the standard reaction (36-39%), indicatingstability of the dipyrromethane to the reaction conditions.

(2) Bis(imino)dipyrromethane 3a was treated with Zn(OAc)₂ at roomtemperature for a period (1 to 30 min) prior to the addition ofdipyrromethane 1b, and then refluxing for 2 h (Table 7, Entries 3-6). Nochange in yield from that of the standard reaction was observed,indicating the ability to form porphyrin from the complex (3a)₂Zn₂.

(3) A mixture of bis(imino)dipyrromethane 3a and Zn(OAc)₂ was refluxedfor a period (1 to 30 min) prior to the addition of dipyrromethane 1b,and then refluxing for 2 h (Table 7, Entries 7-11). The yield ofporphyrin declined as the former reaction time was extended: 10 min(35%); 30 min (29%); 1 h (23%); 2 h (21%); 24 h (2%). The reflux periodconverts (3a)₂Zn₂ to (5a)₂Zn and high molecular weight material. Thus,bis(dipyrrinato)zinc(II) complex (5a)₂Zn is not an intermediate alongthe path to porphyrin, whereas (3a)₂Zn₂ is a viable precursor to theporphyrin (either by direct reaction with a dipyrromethane or byreversion to 3a).

TABLE 7 Effects on the order of the addition of substrate and reagent information of porphyrin Zn4ab^(a) 1^(st) step 2^(nd) step Yield EntryReagents Time (temp) Reagents Time (temp) (%)^(b) 1 1b + 3a 30 min (rt)Zn(OAc)₂ 2 h (reflux) 40 2 1b + 30 min (rt) 3a 2 h (reflux) 40 Zn(OAc)₂3 3a + 1 min (rt) 1b 2 h (reflux) 36 Zn(OAc)₂ 4 3 min (rt) 36 5 10 min(rt) 39 6 30 min (rt) 38 7 3a + 10 min (reflux) 1b 2 h (reflux) 35Zn(OAc)₂ 8 30 min (reflux) 29 9 1 h (reflux) 23 10 2 h (reflux) 21 11 24h (reflux) 2 ^(a)Reaction conditions; [3a]and [1b] = 31.6 mM, Zn(OAc)₂(10 equiv) in EtOH. ^(b)The yields of porphyrin were determined usingabsorption spectroscopy. No scrambling was observed in each reaction(LD-MS analysis).

Reversibility of complex (3)₂Zn₂ formation. The reversibility offormation of (3)₂Zn₂ was examined via double-labeling crossover (i.e.,exchange) experiments (Table 8). Three exchange experiments wereperformed using samples of (3a)₂Zn₂ and (3j)₂Zn₂ that were freshlyprepared with a stoichiometric amount of Zn(OAc)₂. (1) Upon dissolving(3a)₂Zn₂ and two mol equiv of 3j in ethanol at room temperature for 20min, LD-MS analysis showed the molecule ion peak corresponding to eachof (3a)₂Zn₂, (3a/3j)Zn₂, and (3j)₂Zn₂, indicating ligand exchange. (2)Analogous treatment of (3j)₂Zn₂ and 3a gave a similar result. (3) Uponmixing equimolar quantities of (3a)₂Zn₂ and (3j)₂Zn₂, again the moleculeion peaks of the two parent complexes and the hybrid complex (3a/3j)Zn₂were observed. These exchange experiments indicate the complexes(3a)₂Zn₂ and (3j)₂Zn₂ form reversibly and readily undergo ligandexchange. Thus, the failure to form porphyrin from non-aryl substitutedbis(imino)dipyrromethanes is not a result of irreversible formation ofthe corresponding complexes (3)₂Zn₂.

TABLE 8 Double-label crossover experiments with complexes (3)₂Zn₂ ^(a)Entry Reactants Products 1 (3a)₂Zn₂ + 3j (3a)₂Zn₂, (3a/3j)Zn₂, (3j)₂Zn₂2 (3j)₂Zn₂ + 3a (3a)₂Zn₂, (3a/3j)Zn₂, (3j)₂Zn₂ 3 (3a)₂Zn₂ + (3j)₂Zn₂(3a)₂Zn₂, (3a/3j)Zn₂, (3j)₂Zn₂ ^(a)Identified by the presence of themolecule ion peak upon LD-MS analysis.

Conclusion. The condensation of a bis(imino)dipyrromethane+adipyrromethane proceeds without a Brønsted acid or an added chemicaloxidant to give the corresponding zinc-porphyrin. Yields of ˜30% aretypical, and reactions at concentrations up to 31.6 mM can be employed.A range of meso-substituents can be introduced under reasonably mildconditions, subject to the proviso that an aromatic group is located atthe 5-position of the bis(imino)dipyrromethane. The availablesubstituent patterns for trans-AB-porphyrins include aryl/alkyl,aryl/aryl, but not alkyl/alkyl groups; for A-porphyrins the substituentmust be aryl (not alkyl). The synthesis of a trans-AB (or A-porphyrinwhere B=H) can be carried out with the A or B substituent on thedipyrromethane or the bis(imino)dipyrromethane. A difference in yieldvia the two approaches reflects differences in the condensation process,given that both routes should give the same porphyrinogen. In thiscontext, the failure of reactions with alkyl- or H-substitutedbis(imino)dipyrromethanes is believed to result from ineffectivecondensation rather than oxidation processes. In summary, the routesdescribed herein should broaden the scope of available trans-AB- andA-porphyrins, and can be applied where needed to the synthesis oftrans-A₂-porphyrins.

Experimental

General. All ¹H NMR (400 MHz) and ¹³C NMR (100 MHz) spectra wereobtained in CDCl₃ unless noted otherwise. Porphyrins were analyzed bylaser desorption mass spectrometry without a matrix (LD-MS) [37]. Fastatom bombardment mass spectrometry (FAB-MS) data are reported for themolecule ion or protonated molecule ion. Absorption spectra wereobtained in THF (zinc porphyrins) or CH₂Cl₂ [bis(imino)dipyrromethane]at room temperature. Column chromatography was performed with flashsilica.

Noncommercial compounds. The dipyrromethanes 1a [27], 1b [28], 1c [29],1d [30], 1e [31], 1f [29], 1g [32], 1h [28], 1i [22], 1j [33], 1k [21],and 1l [1] were prepared using a new method which entails reaction of analdehyde in 100 equivalents of pyrrole as the solvent containing a Lewisacid (e.g., InCl₃) [34].

Spectroscopic yield determination. Yields of porphyrin-forming reactionswere determined by removal of aliquots from the reaction mixturefollowed by absorption spectroscopy of the oxidized product. Forexample, an ethanol solution of 3a (500 μL, 20.0 mM stock solution, 10.0μmol of 3a) and an ethanol solution of 1b (500 μL, 20.0 mM stocksolution, 10.0 μmol of 1b) were combined and treated with Zn(OAc)₂ (18.3mg, 100 μmol), affording [3a]=[1a]=10 mM. The reaction mixture wasrefluxed for a designated period. An aliquot (25 μL) of the reactionmixture was removed and diluted with THF (500 μL, 21 times dilution),then 25 μL of this diluted reaction mixture was added to a cuvettecontaining 3.00 mL of THF (121 times dilution) and the absorptionspectrum was recorded (total dilution 2541 times). The yield of theporphyrin was determined by the intensity of the Soret band (412 nm,ε=500,000 M⁻¹ cm⁻¹) measured from the apex to the base of the red edgeof the band. In this manner, a Soret band absorption of 1.00 wouldcorrespond to a porphyrin yield of 51%.

General Procedures

(A) Diformylation and tin complexation, exemplified fordibutyl(1,9-diformyl-5,10-dihydro-5-phenyldipyrrinato)tin(IV)(Bu₂Sn-2a). A solution of 1a (2.22 g, 10.0 mmol) in DMF (10.0 mL, 128mmol) at 0° C. under argon was treated dropwise with POCl₃ (1.95 mL,21.0 mmol). The mixture was stirred for 1 h at room temperature, andthen was poured into aqueous NaOH (20 mL of a 20% wt solution). Themilky reaction mixture was extracted with CH₂Cl₂. The organic extractswere combined, washed with water, dried (Na₂SO₄), and filtered. Thefiltrate was concentrated to dryness. The resulting crude mixture wasdissolved in CH₂Cl₂ (50 mL), then TEA (4.18 mL, 30.0 mmol) and Bu₂SnCl₂(3.04 g, 10.0 mmol) were added. The mixture was stirred for 30 min atroom temperature. The mixture was concentrated to dryness and passedover a pad of silica and eluted with CH₂Cl₂ containing 1% TEA. Theeluent was concentrated to dryness. The residue was dissolved in aminimum amount of diethyl ether. Then methanol was added, yielding aprecipitate, which upon filtration afforded a pink solid (2.96 g, 58%):mp 96-98° C.; ¹H NMR δ 0.73 (t, J=8.0 Hz, 3H), 0.77 (t, J=8.0 Hz, 3H),1.13-1.62 (m, 12H), 5.53 (s, 1H), 6.13-6.15 (m, 2H), 7.06 (d, J=4.0 Hz,2H), 7.12-7.28 (m, 5H) 9.16 (s, 2H); ¹³C NMR δ 13.70, 13.76, 24.1, 24.6,26.2, 26.5, 27.27, 27.32, 45.4, 115.7, 124.1, 127.1, 128.2, 128.9,138.1, 143.8, 152.2, 178.8. Anal. Calcd for C₂₅H₃₀N₂O₂Sn: C, 58.97; H,5.94; N, 5.50. Found: C, 59.08; H, 5.92; N, 5.50.

(B) Decomplexation of a diformyldipyrromethane-tin complex, exemplifiedfor 1,9-diformyl-5-phenyldipyrromethane (2a). The solution of Bu₂Sn-2a(509 mg, 1.00 mmol) in CH₂Cl₂ (10 mL) was reacted with TFA (116 μL, 1.50mmol) for 10 min at room temperature. The solution was concentrated andchromatographed [silica, hexanes/ethyl acetate (1:1)] affording a palebrown solid (220 mg, 79%): mp 159-160° C. (154-156° C. [12]); ¹H NMR δ5.58 (s, 1H), 6.06-6.08 (m, 2H), 6.87-6.89 (m, 2H), 7.62-7.38 (m, 5H),9.18 (s, 2H), 10.59-10.65 (br, 2H); ¹³C NMR δ 44.7, 112.0, 122.8, 127.9,128.7, 129.2, 132.8, 139.4, 142.2, 179.3; Anal. Calcd for C₁₇H₁₄N₂O₂: C,73.37; H, 5.07; N, 10.07. Found: C, 72.77; H, 5.12; N, 9.85; λ_(abs)(CH₂Cl₂) 303 nm

(C) Direct diformylation of a dipyrromethane, exemplified for1,9-diformyl-5-(pentafluorophenyl)dipyrromethane (2e). A solution of le(3.12 g, 10.0 mmol) in DMF (10.0 mL, 128 mmol) at 0° C. under argon wastreated dropwise with POCl₃ (1.95 mL, 21.0 mmol). The mixture wasstirred for 1 h at room temperature, and then was poured into saturatedaqueous NaOAc (100 mL). The milky reaction mixture was extracted withCH₂Cl₂. The organic extracts were combined, washed with water, dried(Na₂SO₄), and filtered. Removal of the solvent and chromatography[silica, ethyl acetate/CH₂Cl₂ (1:3)] afforded a brown solid (3.14 g,85%): mp 180-182° C.; ¹H NMR δ 6.06 (s, 1H), 6.12-6.14 (m, 2H),6.88-6.90 (m, 2H), 9.21 (s, 2H), 10.94 (br, 2H); ¹³C NMR δ 33.4, 111.5,122.5, 133.0, 137.6.0, 179.3. Anal. Calcd for C₁₇H₉F₅N₂O₂: C, 55.45; H,2.46; N, 7.61. Found: C, 55.47; H, 2.45; N, 7.66.

(D) Imination of a 1,9-diformyldipyrromethane, exemplified for1,9-bis[(propylimino)methyl]-5-phenyldipyrromethane (3a). A solution of2a (83.5 mg, 0.300 mmol) and n-propylamine (500 μL, 6.08 mmol) in THF (1mL) was stirred at room temperature for 1 h. Removal of the solvent andexcess n-propylamine gave a purple solid (102 mg, quantitative): mp101-105° C.; ¹H NMR δ 0.88 (t, J=7.2 Hz, 6H), 1.52-1.62 (m, 4H), 3.37(t, J=7.2 Hz, 4H), 5.42 (s, 1H), 5.87-5.88 (m, 2H), 6.32-6.34 (m, 2H),7.17-7.32 (m, 5H), 7.86 (s, 2H), 8.31-8.68 (br, 2H); ¹³C NMR δ 12.0,24.5, 44.6, 62.7, 109.5, 114.8, 127.3, 128.7, 128.9, 130.3, 136.8,141.2, 151.6; FAB-MS obsd 361.2385; calcd 361.2392 [(M+H)⁺, M=C₂₃H₂₈N₄];λ_(abs) (CH₂Cl₂) 286 nm.

(E) Imination of a 1,9-diformyldipyrromethane-tin complex, exemplifiedfor 1,9-Bis[(propylimino)methyl]-5-phenyldipyrromethane (3a): A mixtureof Bu₂Sn-2a (50.0 mg, 98.2 μmol) and n-propylamine (0.161 mL, 1.96 mmol)was stirred for 2 h at room temperature. The excess n-propylamine wasevaporated to give the title compound as a pink oil (34.0 mg,quantitative) with satisfactory characterization data.

(F) Porphyrin formation, exemplified forZn(II)-5-(4-methylphenyl)-15-phenylporphyrin (Zn4ab). A solution of 3a[prepared from 2a (83.5 mg, 0.300 mmol) in situ] and5-(p-tolyl)dipyrromethane (1b, 70.8 mg, 0.300 mmol) in ethanol (30 mL)was treated with Zn(OAc)₂ (550 mg, 3.00 mmol) under reflux for 18 h. Thesolvent was removed in vacuo, affording a dark purple residue. TLCanalysis [silica, hexanes/CH₂Cl₂ (1:2)] showed the porphyrin as the solemobile species, and dark byproducts at the origin. Chromatography of theresidue over a short pad of silica [hexanes/CH₂Cl₂ (1:2)] afforded apurple solid (60.0 mg, 37%): ¹H NMR δ 2.75 (s, 2H), 7.58-7.62 (m, 2H),7.77-7.83 (m, 2H), 8.13-8.18 (m, 2H), 8.26-8.29 (m, 2H), 9.11-9.15 (m,2H), 9.15-9.19 (m, 2H), 9.41-9.47 (m, 2H), 10.31 (s, 2H); ¹³C NMR δ21.7, 106.6, 120.3, 120.6, 127.4, 128.1, 128.2, 132.2, 132.3, 132.7,132.9, 135.68, 135.78, 137.8, 141.6, 144.6, 150.61, 150.64, 151.0,151.2; LD-MS obsd 538.5; FAB-MS obsd 538.1150, calcd 538.1136(C₃₃H₂₂N₄Zn); λ_(abs) (THF) 413, 539, 573 nm.

(G) Chromatography-free isolation procedure. The ability to isolate thetrans-AB-porphyrin without resort to chromatography is attractive forscale-up purposes. The synthesis of a trans-AB-porphyrin (Zn4ab) wasperformed in the standard manner using 1.0 mmol of reactants. Afterreflux for 18 h, the crude reaction mixture was concentrated to dryness.The residue was washed with diethyl ether and filtered to remove theexcess zinc acetate and pyrrolic polymer byproducts. The filtrate wasconcentrated to dryness. The residue was washed with diethyl ether andthe sparingly soluble polymer byproducts were removed by filtration. Thefiltrate was concentrated. The procedure was repeated ten times. Theresulting crude porphyrin was recrystallized from CH₂Cl₂/cyclohexaneaffording pure porphyrin Zn4ab (105 mg, 31%). The absence of an addedchemical oxidant greatly facilitated purification.

Synthesis.

Dibutyl(1,9-diformyl-5,10-dihydro-5-mesityIdipyrrinato)tin(IV)(Bu₂Sn-2c). Following procedure A with slight modification (formylationwas carried out at 80° C. instead of room temperature, NaOAc was usedinstead of NaOH), reaction of 10.0 mmol of 1c afforded a pink solid(3.69 g, 67%): mp 137-139° C.; ¹H NMR δ 0.75 (t, J=8.0 Hz, 3H), 0.81 (t,J=8.0 Hz, 3H), 1.18-1.65 (m, 15H), 2.30 (s, 3H), 2.48 (s, 3H),5.80-5.82(m, 2H), 5.83 (s, 1H), 6.78 (s, 1H), 6.97 (s, 1H), 7.03 (d,J=4.0 Hz, 2H), 9.13 (s, 2H); ¹³C NMR δ 13.75, 13.77, 20.2, 20.91, 21.14,23.6, 24.8, 26.47, 26.68, 27.51, 27.58, 39.7, 114.5, 124.3, 129.0,130.9, 136.01, 136.13, 136.8, 137.7, 138.1, 152.7, 178.2. Anal. Calcdfor C₂₈H₃₆N₂O₂Sn: C, 61.00; H, 6.58; N, 5.08. Found: C, 61.16; H, 6.63;N. 4.93.

Dibutyl[1,9-diformyl-5,10-dihydro-5-(4-methoxyphenyl)dipyrrinato]tin(IV)(Bu₂Sn-2d). Following procedure A, reaction of 5.00 mmol of 1d affordeda pink solid (1.43 g, 53%): mp 90-92° C.; ¹H NMR δ 0.73 (t, J=8.0 Hz,3H,), 0.77 (t, J=8.0 Hz, 3H), 1.14-1.58 (m, 12H), 3.76 (s, 3H), 5.47 (s,1H), 6.13 (d, J=4.0 Hz, 2H), 6.80 (d, J=8.0 Hz, 2H), 7.03-7.06 (m, 4H),9.15 (s, 2H); ¹³C NMR δ 13.71, 13.76, 24.1, 24.5, 27.27, 27.30, 44.6,55.4, 114.3, 115.6, 124.1, 129.3, 135.9, 138.1, 152.7, 158.6, 178.7.Anal. Calcd for C₂₆H₃₂N₂O₃Sn: C, 57.91; H, 5.98; N, 5.19. Found: C,57.94; H, 5.96; N, 5.18.

1,9-Diformyl-5-(4-methoxyphenyl)dipyrromethane (2d). Following procedureB, reaction of 1.00 mmol of Bu₂Sn-2d afforded a white solid (253 mg,82%): mp 193-195° C. (197-199° C. [14]); ¹H NMR δ 3.81 (s, 3H), 5.51 (s,1H), 6.06-6.08 (m, 2H), 6.87-6.89 (m, 4H), 7.16-7.18 (m, 2H), 9.25 (s,2H), 10.07-10.15 (br, 2H); ¹³C NMR δ 43.8, 55.5, 111.6, 114.7, 122.3,129.7, 131.2, 132.8, 141.7, 159.3, 179.1. Anal. Calcd for C₁₈H₁₆N₂O₃: C,70.12; H, 5.23; N, 9.09. Found: C, 70.18; H, 5.28; N, 8.94.

Dibutyl[1,9-diformyl-5,10-dihydro-5-(4-iodophenyl)dipyrrinato]tin(IV)(Bu₂Sn-2f). Following procedure A, reaction of 10.0 mmol of 1f affordeda dark pink solid (2.92 g, 46%): mp 130-132° C.; ¹H NMR δ 0.72 (t, J=8.0Hz, 3H), 0.78 (t, J=8.0 Hz, 3H), 1.12-1.58 (m, 12H), 5.47 (s, 1H), 6.13(d, J=4.0 Hz, 2H), 6.87 (d, J=8.0 Hz, 2H), 7.06 (d, J=4.0 Hz, 2H), 7.58(d, J=8.0 Hz, 2H), 9.17 (s, 2H); ¹³C NMR δ 13.66, 13.76, 24.1, 24.7,26.2, 26.5, 27.22, 27.34, 44.9, 92.5, 115.6, 124.1, 130.2, 138.2, 143.5,151.3, 179.0. Anal. Calcd for C₂₅H₃₀N₂O₂Sn: C, 47.28; H. 4.60; N, 4.41.Found: C, 47.49; H, 4.68; N, 4.35.

1,9-Diformyl-5-(4-iodophenyl)dipyrromethane (2f). Following procedure B.reaction of 1.00 mmol of Bu₂Sn-2f afforded a brown solid (348 mg, 86%):mp 170-172° C.; ¹H NMR δ 5.53 (s, 1H), 6.06-6.08 (m, 2H), 6.91-6.93 (m,2H), 7.01-7.05 (m, 2H), 7.65-7.69 (m, 2H), 9.16 (s, 2H), 10.59-10.67(br, 2H); ¹³C NMR δ 44.3, 93.6, 112.0, 122.4, 130.7, 138.3, 139.2,141.0, 179.3. Anal. Calcd for C₁₇H₁₃N₂O₂: C, 50.51; H, 3.24; N, 6.93.Found: C, 50.48; H, 3.16; N, 6.87.

1,9-Diformyl-5-methyldipyrromethane (2g). Following procedure C withslight modification (NaOH was used instead of NaOAc), reaction of 2.00mmol of 1 g afforded a pale yellow solid (337 mg, 78%): mp 151-153° C.;¹H NMR δ 1.75 (d, J=7.3 Hz, 3H), 4.38 (q, J=7.3, 14.6 Hz, 1H), 6.20-6.23(m, 2H), 6.92-6.95 (m, 2H), 9.42 (s, 2H), 10.89-11.18 (br, 2H); ¹³C NMRδ 19.0, 32.6, 109.1, 123.4, 132.8, 144.2, 179.6. Anal. Calcd forC₁₂H₁₂N₂O₂: C, 66.65; H, 5.59; N, 12.96. Found: C, 66.53; H, 5.67; N.13.02.

Dibutyl(1,9-diformyl-5,10-dihydro-5-n-pentyldipyrrinato)tin(IV)(Bu₂Sn-2h). Following procedure A, reaction of 10.0 mmol of 1 h affordeda brown viscous liquid (2.11 g, 42%): ¹H NMR δ 0.64-1.82 (m, 29H), 4.35(t, J=6.0 Hz, 1H), 6.33 (d, J=3.6 Hz, 2H), 7.10 (d, J=3.6 Hz, 2H), 9.13(s, 2H); ¹³C NMR δ 13.64, 13.78, 14.21, 14.35, 22.6, 22.8, 23.4, 25.2,26.1, 26.3, 26.7, 27.1, 27.3, 27.5, 31.82, 31.84, 39.2, 41.7, 114.5,124.1, 138.1, 153.5, 178.3; FAB-MS obsd 505.1850, calcd 505.1877[(M+H)⁺, M=C₂₄H₃₆N₂O₂Sn].

1,9-Diformyl-5-n-pentyldipyrromethane (2h). Following procedure B,reaction of 1.00 mmol of Bu₂Sn-2h afforded a brown viscous liquid (196mg, 72%): ¹H NMR δ 0.85, (t, J=7.6 Hz, 3H), 1.27-1.30 (m, 6H), 2.13-2.15(m, 2H), 4.19 (t, J=7.6 Hz, 1H), 6.21-6.23 (m, 2H), 6.96-6.98 (m, 2H),9.41 (s, 2H), 11.22 (br, 2H); ¹³C NMR δ 14.2, 22.6, 27.5, 31.6, 33.5,38.8, 110.0, 124.0, 132.7, 143.6, 179.6; FAB-MS obsd 273.1577, calcd273.1603 [(M+H)⁺, M=C₁₆H₂₀N₂O₂].

Alternatively, following procedure C with slight modification (NaOH wasused instead of NaOAc), reaction of 3.00 mmol of 1 h afforded a brownviscous liquid (588 mg, 72%) with satisfactory characterization data.

1,9-Diformyl-5-(tridec-7-yl)dipyrromethane (2i). Following procedure Cwith slight modification (NaOH was used instead of NaOAc), reaction of1.00 mmol of 1i afforded a pale yellow solid (179 mg, 47%): mp 86-88°C.; ¹H NMR δ 0.83 (t, J=7.1 Hz, 6H), 1.09-1.32 (m, 20H), 2.33-2.40 (m,1H), 4.09 (d, J=10.7 Hz, 1H), 6.17-6.21 (m, 2H), 6.92-6.96 (m, 2H), 9.45(s, 2H), 11.16-11.32 (br, 2H); ¹³C NMR δ 14.3, 22.8, 25.6, 29.6, 30.6,31.9, 40.8, 43.5, 111.4, 123.7, 133.1, 142.9, 179.5; Anal. Calcd forC₂₄H₃₆N₂O₂: C, 74.96; H, 9.44; N, 7.28. Found: C, 74.82; H, 9.47; N,7.27.

1,9-Diformyldipyrromethane (2j). Following procedure C with slightmodification (formylation was carried out at 80° C. instead of roomtemperature), reaction of 10.0 mmol of 1j afforded a pale yellow solid(707 mg, 70%): mp 227-229° C. (229-231° C. [37]); ¹H NMR (THF-d₈) δ3.13-3.17 (m, 2H), 5.54-5.57 (m, 2H), 6.33-6.36 (m, 2H), 8.93 (s, 1H),10.64-10.97 (br, 2H); ¹³C NMR (THF-d₈) δ 26.3, 109.4, 120.6, 133.5,137.8, 177.6; FAB-MS obsd 203.0807, calcd 203.0821 [(M+H)⁺,M=C₁₁H₁₀N₂O₂].

1,9-Bis[(phenylimino)methyl]dipyrromethane (3a-Ph). A solution of 2a(278 mg, 1.00 mmol) and aniline (182 μL, 2.00 mmol) in CH₂Cl₂ (6.7 mL)was treated with TFA (154 μL, 2.00 mmol) at room temperature for 30 min.Triethylamine (418 μL, 3.00 mmol) was added and the reaction mixture wasconcentrated to dryness. Column chromatography [silica, hexanes/ethylacetate/TEA (66:33:1)] afforded a pale purple solid (330 mg, 77%): mp138-141° C.; ¹H NMR δ 5.06-5.21 (m, 1H), 6.52-6.56 (m, 2H), 6.74-6.92(m, 2H), 7.07-7.47 (m, 15H), 8.13 (s, 2H), 9.84-10.78 (br, 2H); ¹³C NMRδ 44.5, 110.4, 117.3, 121.3, 125.6, 127.0, 128.5, 128.7, 129.3, 131.1,138.5, 140.7, 149.6, 151.3. Anal. Calcd for C₂₉H₂₉N₄: C, 81.28; H, 5.65;N, 13.07. Found: C, 81.31; H, 5.74; N, 13.02.

1,9-Bis[(p-anisylimino)methyl]dipyrromethane (3a-An). A solution of 2a(278 mg, 1.00 mmol) and p-anisidine (246 mg, 2.00 mmol) in CH₂Cl₂ (6.7mL) was treated with TFA (154 μL, 2.00 mmol) at room temperature for 30min. Triethylamine (558 μL, 4.00 mmol) was added and the reactionmixture was concentrated to dryness. Column chromatography [silica,hexanes/ethyl acetate/TEA (66:33:1)] afforded a pale purple solid (338mg, 69%): mp 85-87° C.; ¹H NMR δ 3.81 (s, 6H), 5.17-5.20 (m, 1H),5.79-5.82 (m, 2H), 6.48-6.52 (m, 2H), 6.83-6.88 (m, 4H), 6.89-6.95 (m,2H), 7.10-7.14 (m, 2H), 7.15-7.19 (m, 2H), 8.11 (s, 2H); ¹³C NMR δ 44.1,55.5, 109.9, 114.3, 116.4, 122.1, 126.5, 128.19, 128.26, 131.07, 138.2,140.8, 144.1, 147.8, 157.6; FAB-MS obsd 489.2291, calcd 489.2289[(M+H)⁺, M=C₃₁H₂₈N₄O₂].

1,9-Bis[(benzylimino)methyl]dipyrromethane (3a-Bz). A solution of 2a(139 mg, 0.500 mmol) and benzylamine (109 μL, 1.00 mmol) in THF (1 mL)was stirred at room temperature for 2 h. Removal of the solvent gave apurple solid (210 mg, quantitative, estimated 95% pure by ¹H NMRspectroscopy): ¹H NMR δ 4.65 (s, 4H), 5.38 (s, 1H), 5.91-5.93 (m, 2H),6.40-5.42 (m, 2H), 7.16-7.35 (m, 15H), 8.04 (s, 2H); ¹³C NMR δ 44.4,64.3, 109.6, 115.9, 127.04, 127.16, 128.2, 128.5, 128.7, 137.5, 139.4,152.9 (three carbons corresponding to the phenyl unit are missing due tooverlap); FAB-MS obsd 457.2385, calcd 457.2385 [(M+H)⁺, M=C₃₁H₂₈N₄].

Zn(II)-5-(4-Methylphenyl)-15-phenylporphyrin (Zn4ab). Followingprocedure F, reaction of 0.300 mmol of 2a and 1b afforded a purple solid(10.0 mg, 6%) of Zn4ab with satisfactory characterization data.

Zn(II)-5-(4-Methoxyphenyl)-15-(pentafluorophenyl)porphyrin (Zn4de).Following procedure F, reaction of 0.300 mmol of 3d (prepared from 2d insitu) and 1e afforded a purple solid (58 mg, 30%): ¹H NMR δ 4.14 (s,3H), 7.34 (d, J=8.0 Hz, 2H), 8.17 (d, J=8.0 Hz, 2H), 9.05 (d, J=4.0 Hz,2H), 9.20 (d, J=4.0 Hz, 2H), 9.45 (d, J=4.0 Hz, 2H), 9.53 (d, J=4.0 Hz,2H), 10.36 (s, 2H); ¹³C NMR (THF-d₈) δ 55.9, 99.9, 107.2, 113.0, 122.3,130.8, 132.4, 133.5, 133.9, 136.3, 136.7, 150.6, 150.8, 151.1, 151.4,160.8; LD-MS obsd 644.4; FAB-MS obsd 644.0645, calcd 644.0614(C₃₃H₁₇F₅N₄OZn); λ_(abs) (THF) 413, 539, 574 nm. Alternatively, reactionof 0.500 mmol of 3e (prepared from 2e in situ) and 1d afforded a purplesolid (103 mg, 32%) of Zn4de with satisfactory analytical data.

Zn(II)-5-Ethoxycarbonyl-15-(4-iodophenyl)porphyrin (Zn4fk). Followingprocedure F, reaction of 0.500 mmol of 3f (prepared from 2f in situ) and1k afforded a purple solid (124 mg, 38%): ¹H NMR δ 1.82 (t, J=8.0 Hz,3H), 5.08 (q, J=8.0 Hz, 2H), 8.01 (d, J=8.0 Hz, 2H), 8.17 (d, J=8.0 Hz,2H), 9.04 (d, J=4.0 Hz, 2H), 9.42 (d, J=4.0 Hz, 2H), 9.50 (d, J=4.0 Hz,2H), 9.67 (d, J=4.0 Hz, 2H), 10.32 (s, 2H); ¹³C NMR (THF-d₈) δ 15.4,63.2, 94.6, 107.4, 109.6, 121.2, 132.3, 132.5, 133.0, 133.6, 136.7,137.4, 143.9, 150.10, 150.12, 150.21, 150.86, 150.88, 151.1, 172.6;LD-MS obsd 646.2; FAB-MS obsd 646.9932, calcd 646.9922 (C₂₉H₁₉IN₄O₂Zn);λ_(abs) (THF) 412, 538, 574 nm.

Zn(II)-5,15-Diphenylporphyrin (Zn4aa). Following procedure F, reactionof 0.500 mmol of 3a (prepared from 2a in situ) and 1a afforded a purplesolid (94.6 mg, 36%): ¹H NMR (THF-d₈) δ 7.78-7.80 (m, 6H), 8.24-8.27 (m,4H), 9.03 (d, J=4.0 Hz, 4H), 9.41 (d, J=4.0 Hz, 4H), 10.28 (s, 2H); ¹³CNMR (THF-d₈) δ 106.6, 120.4, 127.4, 128.2, 132.4, 132.8, 135.8, 144.6,150.6, 151.0; LD-MS obsd 523.5; FAB-MS obsd 524.1007, calcd 524.0979(C₃₂H₂₀N₄Zn); λ_(abs) (THF) 412, 538, 573 nm.

Zn(II)-5-Mesitylporphyrin (Zn4cj). Following procedure F, reaction of0.500 mmol of 3c (prepared from Bu₂Sn-2c in situ) and 1j afforded apurple solid (93.5 mg, 38%): ¹H NMR (THF-d₈) δ 1.82 (s, 6H), 2.65 (s,3H), 7.34 (s, 2H), 8.87 (d, J=4.0 Hz, 2H), 9.38 (d, J=4.0 Hz, 2H), 9.50(s, 4H), 10.25 (s, 2H), 10.26 (s, 1H); ¹³C NMR (THF-d₈) δ 21.7, 22.2,104.9, 105.6, 118.5, 128.6, 131.3, 132.68, 132.81, 138.2, 140.1, 140.8,150.2, 150.54, 150.63, 151.0; LD-MS obsd 489.6; FAB-MS obsd 490.1146,calcd 490.1136 (C₂₉H₂₂N₄Zn); λ_(abs) (THF) 406, 532, 566 nm. Attempts tocarry out the reaction of 0.250 mmol of 3j (prepared from 2j in situ)and 1c did not afforded the desired porphyrin.

Zn(II)-5-n-Pentyl-15-phenylporphyrin (Zn4ah). Following procedure F,reaction of 0.100 mmol of 3a (prepared from 2a in situ) and 1h affordeda purple solid (16.6 mg, 32%): ¹H NMR δ 1.00 (t, J=7.2 Hz, 3H),1.57-1.62 (m, 2H), 1.86-1.89 (m, 2H), 2.61-2.64 (m, 2H), 5.20 (t, J=8.0Hz, 3H), 7.75-7.77 (m, 3H), 8.20-8.23 (m, 2H), 8.96 (d, J=4.0 Hz, 2H),9.34 (d, J=4.0 Hz, 2H), 9.45 (d, J=4.0 Hz, 2H), 9.76 (d, J=4.0 Hz, 2H),10.18 (s, 1H); ¹³C NMR δ 14.7, 23.9, 33.9, 36.4, 40.2, 106.1, 120.7,127.4, 128.1, 130.0, 132.3, 132.52, 132.64, 135.7, 144.7, 150.17,150.29, 151.11, 151.18; LD-MS obsd 517.8; FAB-MS obsd 518.1458, calcd518.1449 [(M+H)⁺, M=C₂₉H₂₂N₄Zn]; λ_(abs) (THF) 412, 540, 574 nm.Attempts to carry out the reaction of 0.25 mmol of 3h (prepared from 2hin situ) and 1a did not afforded the desired porphyrin.

Studies Probing the Reaction Course.

Stability of bis(imino)dipyrromethanes. A 1,9-diformyldipyrromethanetypically affords a pale yellow solution in ethanol. Treatment withn-propylamine affords the bis(imino)dipyrromethane 3 as a pale orangesolution, and upon isolation, a pale orange solid. On standing, thesolution (or solid) turns purple over the course of a few hours (ordays). The ¹H NMR spectrum showed diminution of the resonancescorresponding to 3a and growth of resonances associated with thedipyrrin 5a. The singlet (5.42 ppm) corresponding to the 5-position ofthe dipyrromethane had vanished, the singlet corresponding to the imineproton shifted from 7.86 ppm to 8.32 ppm, and two multipletscorresponding to the β-pyrrolic protons shifted from 5.87 ppm and 6.33ppm to 6.62 and 6.80 ppm, respectively. The absorption spectrum of themixture showed a strong absorption at 481 nm, as expected for thedipyrrin framework [43]. Attempts to analyze the reaction mixture by TLCwere not fruitful owing to the very high polarity of the startingbis(imino)dipyrromethane 3a. Note that the conversion of 3a→5a may bequite limited yet the solution appears deeply colored. By contrast, thebis(imino)dipyrromethanes bearing an alkyl substituent or no substituent(e.g., 3j) were resistant to oxidation; thus, the formation of thecorresponding bis(imino)dipyrrin (e.g., 5j) was not observed at roomtemperature over the course of 24 h.

Observation of complexes (3)₂Zn₂ during porphyrin-forming reactions. Ingeneral, the treatment of a bis(imino)dipyrromethane with Zn(OAc)₂ inthe absence of a dipyrromethane afforded the zinc complex, regardless ofthe nature of the meso substituent. During attempted porphyrin formationin the presence of a dipyrromethane, however, the observation of complex(3)₂Zn₂ depends on both the concentration of the reaction and the natureof the substituent. (1) Concentration: LD-MS analysis of a sample fromthe crude reaction mixture performed at 10 or 31.6 mM typically gave thepeak expected for the zinc porphyrin (m/z=538.5 for Zn4ab. derived from3a+1b) with the absence of any peak due to (3a)₂Zn₂. When reaction wascarried out at higher concentration (100 or 316 mM, instead of 10 or31.6 mM), the expected molecule ion peak of the porphyrin was typicallyaccompanied by the peak at m/z=844.0 due to (3a)₂Zn₂. (2) Substituents:For aryl-substituted bis(imino)dipyrromethanes, the reactions at 10.0 or31.6 mM proceeded well and no complex was observed. However, thereactions of bis(imino)dipyrromethane 3j or 5-alkyl substitutedbis(imino)dipyrromethane 3l proceeded poorly, and the peak (m/z=692.3for 3j, 832.6 for 3l) corresponding to the complex analogous to (3a)₂Zn₂was observed. The complex (3j)₂Zn₂ forms reversibly (vide infra); thus,the formation of the complexes does not appear to be the source of thefailure to form the corresponding porphyrin.

Isolation of (3a)₂Zn₂. A solution of 3a (200 μmol, prepared from 2a insitu) in ethanol (10 mL) was treated with Zn(OAc)₂ (36.6 mg, 100 μmol)for 10 min. The reaction mixture was concentrated to dryness, affording(3a)₂Zn₂ quantitatively: ¹H NMR δ 1.12 (t, J=7.2 Hz, 12H), 1.71-1.85 (m,8H), 3.37-3.47 (m, 8H), 5.55-5.59 (m, 2H), 6.24-6.28 (m, 4H), 6.94-6.99(m, 4H), 7.20-7.38 (m, 14H); λ_(abs) (CH₂Cl₂) 333 nm; FAB-MS obsd845.2923; calcd 845.2976 [(M+H)⁺, M=C₄₆H₅₂N₈Zn₂]. Prolonged examinationof the sample by FAB-MS (3-nitrobenzyl alcohol matrix) resulted inalteration of the pattern of peaks in the molecule-ion region.Electron-impact mass spectrometry as well as LD-MS analysis (without amatrix) afforded a rich isotopic distribution in close agreement withexpectation owing to the presence of two zinc atoms. Attempts tochromatograph or obtain crystals of (3a)₂Zn₂ (also for (3j)₂Zn₂ and(31)₂Zn₂) were to no avail. The failure to obtain crystals may stem fromseveral factors, including the presence of stereoisomers, susceptibilityto oxidation, and relatively weak complexes.

Demetalation of (3a)₂Zn₂. A solution of (3a)₂Zn₂ (100 μmol, preparedfrom 3a in situ) in CH₂Cl₂ (10 mL) was washed with water (10 mL). Theorganic phase was dried and concentrated to dryness. ¹H NMR spectroscopyof the residue showed demetalation of (3a)₂Zn₂ to 3a (>60%), togetherwith the formation of unknown species.

Isolation of bis(dipyrrinato)Zn(II) complex [(5a)₂Zn]. A solution of(3a)₂Zn₂ (200 μmol, prepared from 3a in situ) in ethanol (10 mL) wasrefluxed for 2 days. The reaction mixture was concentrated to dryness.The residue was precipitated with CH₂Cl₂/hexanes and filtered to removethe excess pyrrolic polymer byproducts. The filtrate was concentrated todryness. The residue was washed with hexanes, sonicated, and filtered.The filtrate was concentrated. The procedure was repeated ˜10 times,affording a purple solid (24.8 mg, estimated >85% purity by ¹H NMRspectroscopy): ⁸H NMR δ 0.62-0.66 (m, 12H), 1.19-1.26 (m, 8H), 3.11-3.16(m, 8H), 6.67-6.71 (m, 8H), 7.24-7.53 (m, 10H), 7.99 (s, 1H); LD-MS obsd778.4; FAB-MS obsd 779.3495; calcd 779.3528 [(M+H)⁺, M=C₄₆H₅₂N₈Zn];λ_(abs) (CH₂Cl₂) 545 nm.

Exchange reactions. (A) (3a)₂Zn₂+(3j)₂Zn₂. An ethanol solution of(3a)₂Zn₂ (500 μL, 10.0 mM stock solution freshly prepared from 10.0 μmolof 3a, containing 5.00 μmol of (3a)₂Zn₂) and an ethanol solution of(3j)₂Zn₂ (500 μL, 10.0 mM stock solution freshly prepared from 10.0 μmolof 3j, containing 5.00 μmol of (3j)₂Zn₂) were combined, affording[(3a)₂Zn₂]=[(3j)₂Zn₂]=5.00 mM. The reaction mixture was stirred at roomtemperature for 20 min, and a sample was subjected to LD-MS analysis.LD-MS obsd 692.3, 768.4, 844.4; calcd 692.2 [(3j)₂Zn₂, M=C₄₆H₅₂N₈Zn₂],768.3 [(3a)(3j)Zn₂, M=C₄₆H₅₂N₈Zn₂], 844.3 [(3a)₂Zn₂, M=C₄₆H₅₂N₈Zn₂].

(B) (3a)₂Zn₂+3j. An ethanol solution of (3a)₂Zn₂ (500 μL, 10.0 mM stocksolution freshly prepared from 10.0 μmol of 3a, containing 5.00 μmol of(3a)₂Zn₂) and an ethanol solution of 3j (500 μL, 20.0 mM stock solution,10.0 μmol of 3a) were combined, affording [(3a)₂Zn₂]=5.00 mM, [3j]=10.0mM. The reaction mixture was stirred at room temperature for 10 min, anda sample was subjected to LD-MS analysis. LD-MS obsd 692.0, 768.1,844.1.

(C) 3a+(3j)₂Zn₂. An ethanol solution of (3j)₂Zn₂ (500 μL, 10.0 mM stocksolution freshly prepared from 10.0 μmol of 3j, containing 5.00 μmol of(3j)₂Zn₂) and an ethanol solution of 3a (500 μL, 20.0 mM stock solution,10.0 μmol of 3a) were combined, affording [(3a)₂Zn₂]=5.00 mM, [3j]=10.0mM. The reaction mixture was stirred at room temperature for 10 min, anda sample was subjected to LD-MS analysis: LD-MS obsd 692.2, 768.2,844.2.

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The foregoing is illustrative of the present invention, and is not to beconstrued as limiting thereof. The invention is defined by the followingclaims, with equivalents of the claims to be included therein.

1. A compound of Formula II:

wherein: R is alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl,cycloalkylalkenyl, cycloalkylalkynyl, aryl, arylalkyl, arylalkenyl,arylalkynyl, alkoxy, or acyl; R¹ is H, alkyl or aryl; R², R³, R⁴, and R⁵are each independently selected from the group consisting of H, halo,loweralkoxy, and loweralkylthio; and A is aryl.
 2. The compound of claim1, wherein A is an aromatic hydrophilic group, an aromatic surfaceattachment group, an aromatic cross-coupling group or an aromaticbioconjugatable group.
 3. The compound of claim 2, wherein A is anaromatic alkene, alkyne, alcohol, thiol, selenyl, phosphono, carboxylicacid, formyl, halo or amine containing-group.
 4. The compound of claim1, wherein R², R³, R⁴, and R⁵ are each independently selected from thegroup consisting of H and halo.
 5. The compound of claim 1, wherein R²,R³, R⁴, and R⁵ are each H.
 6. The compound of claim 1, wherein saidcompound has the formula:


7. A method of making a compound of Formula II:

wherein: R is alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl,cycloalkylalkenyl, cycloalkylalkynyl, aryl, arylalkyl, arylalkenyl,arylalkynyl, alkoxy, or acyl; R¹ is H, alkyl or aryl; R², R³, R⁴, and R⁵are each independently selected from the group consisting of H, halo,loweralkoxy, and loweralkylthio; and A is aryl; said method comprising:reacting a dipyrromethane of Formula IV:

wherein A, R¹, R², ⁴ and R⁵ are as given above, with a compound ofFormula V:

wherein R is as given above in an organic solvent to produce saidcompound of Formula II.
 8. The method of claim 7, wherein A is anaromatic surface attachment group, an aromatic cross-coupling group oran aromatic bioconjugatable group.
 9. The method of claim 8, wherein Ais an aromatic alkene, alkyne, alcohol, thiol, selenyl, phosphono,carboxylic acid, formyl, halo or amine containing-group.
 10. The methodof claim 7, wherein R², R³, R⁴, and R⁵ are each independently selectedfrom the group consisting of H and halo.
 11. The method of claim 7,wherein R², R³, R⁴, and R⁵ are each H.
 12. The method of claim 7,wherein said solvent is selected from the group consisting of methylenechloride, chloroform, tetrahydrofuran, nitromethane, toluene,acetonitrile, and mixtures thereof.